System for authenticating objects

ABSTRACT

A system for authenticating an object is disclosed. The system has a sensing device for sensing coded tags printed on the object. Each coded tags encodes an identity of the object and a signature fragment. An entire signature is encoded in multiple coded tags. The system further has a processor for determining a signature fragment identifier associated with respective signature fragments. The processor also generates the entire signature from the signature fragments and associated signature fragment identifiers. The entire signature is then decrypted to obtain a generated identity. By comparing the identity encoded by the coded tags with the generated identity, the object is authenticated.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. application Ser. No.12/247,160 filed on Oct. 7, 2008, which is a continuation of U.S.application Ser. No. 11/041,723 filed on Jan. 25, 2005, now issued U.S.Pat. No. 7,467,300, all of which is herein incorporated by reference.

FIELD OF THE INVENTION

The present invention broadly relates to a method and apparatus for theprotection of products and security documents using machine readabletags disposed on or in a surface of the product or security document.

CO-PENDING APPLICATIONS

The following applications have been filed by the Applicant:

11/041,650 11/041,651 7,506,168 7,441,712 11/041,610 11/041,60911/041,626 7,537,157 11/041,624 7,395,963 7,457,961 11/041,580 7,467,2997,565,542

The disclosures of these co-pending applications are incorporated hereinby reference.

CROSS-REFERENCES

Various methods, systems and apparatus relating to the present inventionare disclosed in the following co-pending applications and grantedpatents filed by the applicant or assignee of the present invention. Thedisclosures of all of these co-pending applications and granted patentsare incorporated herein by cross-reference.

7,249,108 6,566,858 6,331,946 6,246,970 6,442,525 7,346,586 09/505,9516,374,354 7,246,098 6,816,968 6,757,832 6,334,190 6,745,331 7,249,1097,197,642 7,093,139 7,509,292 10/636,283 10/866,608 7,210,038 7,401,22310/940,653 10/942,858 10/815,621 7,243,835 10/815,630 10/815,63710/815,638 7,251,050 10/815,642 7,097,094 7,137,549 10/815,618 7,156,29210/815,635 7,357,323 7,654,454 7,137,566 7,131,596 7,128,265 7,197,3747,175,089 10/815,617 7,537,160 7,178,719 7,506,808 7,207,483 7,296,7377,270,266 10/815,614 7,605,940 7,128,270 7,457,007 7,150,398 7,159,7777,450,273 7,188,769 7,097,106 7,070,110 7,243,849 6,623,101 6,406,1296,505,916 6,457,809 6,550,895 6,457,812 6,428,133 7,204,941 7,282,1647,465,342 7,416,280 6,746,105 7,246,886 7,128,400 7,108,355 6,991,3227,287,836 7,118,197 7,575,298 7,364,269 7,077,493 6,962,402 10/728,8037,147,308 7,524,034 7,118,198 7,168,790 7,172,270 7,229,155 6,830,3187,195,342 7,175,261 7,465,035 7,108,356 7,118,202 7,510,269 7,134,7447,510,270 7,134,743 7,182,439 7,210,768 7,465,036 7,134,745 7,156,4847,118,201 7,111,926 7,431,433 10/944,043 7,156,289 7,178,718 7,225,97909/575,197 7,079,712 6,825,945 7,330,974 6,813,039 7,190,474 6,987,5066,824,044 7,038,797 6,980,318 6,816,274 7,102,772 7,350,236 6,681,0456,678,499 6,679,420 6,963,845 6,976,220 6,728,000 7,110,126 7,173,7226,976,035 6,813,558 6,766,942 6,965,454 6,995,859 7,088,459 6,720,9857,286,113 6,922,779 6,978,019 6,847,883 7,131,058 7,295,839 7,406,4457,533,031 6,959,298 6,973,450 7,150,404 6,965,882 7,233,924 09/575,1817,593,899 7,175,079 7,162,259 6,718,061 7,464,880 7,012,710 6,825,9567,451,115 7,222,098 7,590,561 7,263,508 7,031,010 6,972,864 6,862,1057,009,738 6,989,911 6,982,807 7,518,756 6,829,387 6,714,678 6,644,5456,609,653 6,651,879 10/291,555 7,293,240 7,467,185 7,415,668 7,044,3637,004,390 6,867,880 7,034,953 6,987,581 7,216,224 7,506,153 7,162,2697,162,222 7,290,210 7,293,233 7,293,234 6,850,931 6,865,570 6,847,96110/685,583 7,162,442 10/685,584 7,159,784 7,557,944 7,404,144 6,889,89610/831,232 7,174,056 6,996,274 7,162,088 7,388,985 7,417,759 7,362,4637,259,884 7,167,270 7,388,685 6,986,459 10/954,170 7,181,448 7,590,6227,657,510 7,324,989 7,231,293 7,174,329 7,369,261 7,295,922 7,200,59111/020,106 11/020,260 11/020,321 11/020,319 7,466,436 7,068,3827,007,851 6,957,921 6,457,883 7,044,381 7,094,910 7,091,344 7,122,6857,038,066 7,099,019 7,062,651 6,789,194 6,789,191 7,529,936 7,278,0187,360,089 7,526,647 7,467,416 6,644,642 6,502,614 6,622,999 6,669,3856,827,116 7,011,128 7,416,009 6,549,935 6,987,573 6,727,996 6,591,8846,439,706 6,760,119 7,295,332 7,064,851 6,826,547 6,290,349 6,428,1556,785,016 6,831,682 6,741,871 6,927,871 6,980,306 6,965,439 6,840,6067,036,918 6,977,746 6,970,264 7,068,389 7,093,991 7,190,491 7,511,84710/932,044 10/962,412 7,177,054 7,364,282 10/965,733 10/965,93310/974,742 7,468,809 7,180,609 7,538,793 6,982,798 6,870,966 6,822,6396,474,888 6,627,870 6,724,374 6,788,982 7,263,270 6,788,293 6,946,6726,737,591 7,091,960 7,369,265 6,792,165 7,105,753 6,795,593 6,980,7046,768,821 7,132,612 7,041,916 6,797,895 7,015,901 7,289,882 7,148,64410/778,056 10/778,058 10/778,060 7,515,186 7,567,279 10/778,06210/778,061 10/778,057 7,096,199 7,286,887 7,400,937 7,474,930 7,324,8597,218,978 7,245,294 7,277,085 7,187,370 7,609,410 7,660,490 10/919,3797,019,319 7,593,604 7,660,489 7,043,096 7,055,739 7,233,320 6,830,1966,832,717 7,182,247 7,120,853 7,082,562 6,843,420 10/291,718 6,789,7317,057,608 6,766,944 6,766,945 7,289,103 7,412,651 7,299,969 7,108,1927,111,791 7,077,333 6,983,878 7,564,605 7,134,598 7,431,219 6,929,1866,994,264 7,017,826 7,014,123 7,150,396 7,469,830 7,017,823 7,025,2767,284,701 7,469,062 7,308,148 7,630,554 7,526,128 6,957,768 7,456,8207,170,499 7,106,888 7,123,239 6,982,701 6,982,703 7,227,527 6,786,3976,947,027 6,975,299 7,139,431 7,048,178 7,118,025 6,839,053 7,015,9007,010,147 7,133,557 6,914,593 7,437,671 6,938,826 7,278,566 7,123,2456,992,662 6,593,166 7,132,679 6,940,088 10/727,181 10/727,162 7,377,6087,399,043 7,121,639 7,165,824 7,152,942 10/727,157 7,181,572 7,096,1377,302,592 7,278,034 7,188,282 7,592,829 10/727,180 10/727,179 10/727,19210/727,274 10/727,164 7,523,111 7,573,301 7,660,998 10/754,53610/754,938 10/727,160 7,369,270 6,795,215 7,070,098 7,154,638 6,805,4196,859,289 6,977,751 6,398,332 6,394,573 6,622,923 6,747,760 6,921,14410/884,881 7,092,112 7,192,106 7,374,266 7,427,117 7,448,707 7,281,33010/854,503 7,328,956 10/854,509 7,188,928 7,093,989 7,377,609 7,600,84310/854,498 10/854,511 7,390,071 10/854,525 10/854,526 7,549,7157,252,353 7,607,757 7,267,417 10/854,505 7,517,036 7,275,805 7,314,2617,281,777 7,290,852 7,484,831 10/854,523 10/854,527 7,549,718 10/854,5207,631,190 7,557,941 10/854,499 10/854,501 7,266,661 7,243,193 10/854,51810/934,628 6,454,482 6,808,330 6,527,365 6,474,773 6,550,997 7,093,9236,957,923 7,131,724 7,396,177 7,168,867 7,125,098

BACKGROUND

Currently there are two main types of technologies offering alternativemethods of unique product item identification, such as EPCs, namely:

-   -   2D optical barcodes, and    -   RFID.

A 2D optical barcode consists of a composite image that can store about2,000 bytes of data along two dimensions. The Uniform Code Council andEuropean Article Numbering (EAN) International have standardized a rangeof 2D barcodes, all with a significantly larger data capacity than theexisting EPC.

2D optical barcodes are now widely used in the global pharmaceuticalindustry. In the United States, the Food and Drug Administration (FDA)has mandated their use on all pharmaceutical goods manufactured withinits jurisdiction to identify product lines. The main advantage drivingtheir acceptance is that they are inexpensive to produce.

The main disadvantage of 2D optical barcodes is that they are oftendifficult to read due to label damage and a direct ‘line-of-sight’ isneeded for scanning. In addition to this, 2-D optical barcodes areunsightly and therefore detrimental to the packaging of the product.This problem is exacerbated in the case of pharmaceuticals, whichgenerally use small packaging, but require a relatively large bar-codewhich can therefore obscure a substantial part of the packaging.

In the case RFID tags, these can again provide unique product itemidentification encoded in the form of an EPC. However, there are alsosome disadvantages that make RFID tags unsuitable for some products.

First, RFID tags are costly to produce. Secondly, the presence ofmetals, liquids and other electromagnetic frequency (EMF) signals caninterfere with RFID tag scanners, and thus seriously jeopardize thereliability and integrity of the RFID system. Thirdly tags can be readremotely without knowledge of the tag holder, thereby raising privacyconcerns.

Surface Coding Background

The netpage surface coding consists of a dense planar tiling of tags.Each tag encodes its own location in the plane. Each tag also encodes,in conjunction with adjacent tags, an identifier of the regioncontaining the tag. This region ID is unique among all regions. In thenetpage system the region typically corresponds to the entire extent ofthe tagged surface, such as one side of a sheet of paper.

The surface coding is designed so that an acquisition field of viewlarge enough to guarantee acquisition of an entire tag is large enoughto guarantee acquisition of the ID of the region containing the tag.Acquisition of the tag itself guarantees acquisition of the tag'stwo-dimensional position within the region, as well as othertag-specific data. The surface coding therefore allows a sensing deviceto acquire a region ID and a tag position during a purely localinteraction with a coded surface, e.g. during a “click” or tap on acoded surface with a pen.

The use of netpage surface coding is described in more detail in thefollowing copending patent applications, U.S. Ser. No. 10/815,647(docket number HYG001US), entitled “Obtaining Product Assistance” filedon 2 Apr. 2004; and U.S. Ser. No. 10/815,609 (docket number HYT001US),entitled “Laser Scanner Device for Printed Product Identification Cod”filed on 2 Apr. 2004.

Cryptography Background

Cryptography is used to protect sensitive information, both in storageand in transit, and to authenticate parties to a transaction. There aretwo classes of cryptography in widespread use: secret-key cryptographyand public-key cryptography.

Secret-key cryptography, also referred to as symmetric cryptography,uses the same key to encrypt and decrypt a message. Two parties wishingto exchange messages must first arrange to securely exchange the secretkey.

Public-key cryptography, also referred to as asymmetric cryptography,uses two encryption keys. The two keys are mathematically related insuch a way that any message encrypted using one key can only bedecrypted using the other key. One of these keys is then published,while the other is kept private. They are referred to as the public andprivate key respectively. The public key is used to encrypt any messageintended for the holder of the private key. Once encrypted using thepublic key, a message can only be decrypted using the private key. Thustwo parties can securely exchange messages without first having toexchange a secret key. To ensure that the private key is secure, it isnormal for the holder of the private key to generate the public-privatekey pair.

Public-key cryptography can be used to create a digital signature. Ifthe holder of the private key creates a known hash of a message and thenencrypts the hash using the private key, then anyone can verify that theencrypted hash constitutes the “signature” of the holder of the privatekey with respect to that particular message, simply by decrypting theencrypted hash using the public key and verifying the hash against themessage. If the signature is appended to the message, then the recipientof the message can verify both that the message is genuine and that ithas not been altered in transit.

Secret-key can also be used to create a digital signature, but has thedisadvantage that signature verification can also be performed by aparty privy to the secret key.

To make public-key cryptography work, there has to be a way todistribute public keys which prevents impersonation. This is normallydone using certificates and certificate authorities. A certificateauthority is a trusted third party which authenticates the associationbetween a public key and a person's or other entity's identity. Thecertificate authority verifies the identity by examining identitydocuments etc., and then creates and signs a digital certificatecontaining the identity details and public key. Anyone who trusts thecertificate authority can use the public key in the certificate with ahigh degree of certainty that it is genuine. They just have to verifythat the certificate has indeed been signed by the certificateauthority, whose public key is well-known.

To achieve comparable security to secret-key cryptography, public-keycryptography utilises key lengths an order of magnitude larger, i.e. afew thousand bits compared with a few hundred bits.

Schneier B. (Applied Cryptography, Second Edition, John Wiley & Sons1996) provides a detailed discussion of cryptographic techniques.

SUMMARY OF THE INVENTION

According to an aspect of the present invention there is provided asystem for authenticating an object, the system comprising:

-   -   a sensing device for sensing coded tags printed on the object,        each coded tags encoding an identity of the object and a        signature fragment, an entire signature being encoded in a        plurality of coded tags;    -   a processor for determining a signature fragment identifier        associated with respective signature fragments, for generating        the entire signature from the signature fragments and associated        signature fragment identifiers, for decrypting the entire        signature to obtain a generated identity;    -   means for comparing the identity encoded by the coded tags with        the generated identity; and    -   means for authenticating the object using the results of the        comparison.

Other aspects are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

An example of the present invention will now be described with referenceto the accompanying drawings, in which:—

FIG. 1 is an example of a document including Hyperlabel encoding;

FIG. 2 is an example of a system for interacting with the Hyperlabeldocument of FIG. 1;

FIG. 3 is a further example of system for interacting with theHyperlabel document of FIG. 1;

FIG. 4. is a first example of a tag structure;

FIG. 5. is an example of a symbol unit cell for the tag structure ofFIG. 4;

FIG. 6. is an example of an array of the symbol unit cells of FIG. 5;

FIG. 7. is an example of symbol bit ordering in the unit cells of FIG.5;

FIG. 8. is an example of the tag structure of FIG. 4 with every bit set;

FIG. 9. is an example of tag types within a tag group for the tagstructure of FIG. 4;

FIG. 10. is an example of continuous tiling of the tag groups of FIG. 9;

FIG. 11 is an example of interleaved codewords for the tag structure ofFIG. 4;

FIG. 12 is an example of a code word for the tag structure of FIG. 4;

FIG. 13. is an example of a tag and its eight immediate neighbours, eachlabelled with its corresponding bit index in the active area map;

FIG. 14. is an alternative example of tag types within a tag group forthe tag structure of FIG. 4;

FIG. 15. is an example of continuous tiling of the tag groups of FIG.14;

FIG. 16. is an example of the orientation-indicating cyclic positioncodeword R for the tag group of FIG. 14;

FIG. 17. is an example of a local codeword A for the tag group of FIG.14;

FIG. 18. is an example of distributed codewords B, C, D and E, for thetag group of FIG. 14;

FIG. 19. is an example of a layout of complete tag group;

FIG. 20. is an example of a code word for the tag group of FIG. 14;

FIG. 21. is a second example of a tag structure;

FIG. 22. is an example of a symbol unit cell for the tag structure ofFIG. 21;

FIG. 23. is an example of an array of the symbol unit cells of FIG. 22;

FIG. 24. is an example of symbol bit ordering in the unit cells of FIG.22;

FIG. 25. is an example of the tag structure of FIG. 21 with every bitset;

FIG. 26. is an example of tag types within a tag group for the tagstructure of FIG. 21;

FIG. 27. is an example of continuous tiling of the tag groups of FIG.26;

FIG. 28 is an example of an orientation indicating cyclic positioncodeword for the tag structure of FIG. 21;

FIG. 29 is an example of a codeword for the tag structure of FIG. 21;

FIG. 30 is an example of fragments of distributed codewords for the tagstructure of FIG. 21;

FIG. 31. is an example of continuous tiling of the tag groups of FIG.21;

FIG. 32. is an example of a tag segment of the tag groups of FIG. 21;

FIG. 33. is an example of inter-segment spacing for the tag groups ofFIG. 21;

FIG. 34. is an example of the effect of inter-segment spacing on targetposition for the tag groups of FIG. 21;

FIG. 35. is an example of a code word for the tag group of FIG. 21;

FIG. 36. is an example of tag coordinates for the tag group of FIG. 21;

FIG. 37. is an example of tag and six immediate neighbour tags eachlabelled with its corresponding bit index in the active area map;

FIG. 38. is an example of a contiguous set of tags making up a datablock;

FIG. 39. is an example of an expanded tag structure;

FIG. 40 is an example of a codeword for the tag structure of FIG. 39;

FIG. 41 is an example of fragments of distributed codewords for the tagstructure of FIG. 39;

FIG. 42 is a second example of fragments of distributed codewords forthe tag structure of FIG. 39;

FIG. 43 is an example of an item signature object model;

FIG. 44. is an example of Scanning at Retailer interactions;

FIG. 45. is an example of Online Scanning interaction detail;

FIG. 46. is an example of Offline Scanning interaction details;

FIG. 47. is an example of netpage Pen Scanning interactions;

FIG. 48. is an example of netpage Pen Scanning interaction details;

FIG. 49. is an example of a Hyperlabel tag class diagram;

FIG. 50. is an example of an item ID class diagram;

FIG. 51. is an example of a note ID class diagram

FIG. 52. is an example of a pharmaceutical ID class diagram;

FIG. 53. is an example of an Object Description, ownership andaggregation class diagram;

FIG. 54. is an example of an Object Scanning History class diagram;

FIG. 55. is an example of scanner class diagram;

FIG. 56. is an example of an object ID hot list diagram;

FIG. 57. is an example of a valid ID range class diagram;

FIG. 58. is an example of Public Key List class diagram;

FIG. 59. is an example of a Trusted Authenticator class diagram;

FIG. 60. is an example of Tagging and Tracking Object Management.

DETAILED DESCRIPTION OF THE DRAWINGS

The netpage surface coding consists of a dense planar tiling of tags.Each tag encodes its own location in the plane. Each tag also encodes,in conjunction with adjacent tags, an identifier of the regioncontaining the tag. In the netpage system, the region typicallycorresponds to the entire extent of the tagged surface, such as one sideof a sheet of paper.

Hyperlabel is the adaptation of the netpage tags for use in unique itemidentification for a wide variety of applications, including securitydocument protection, object tracking, pharmaceutical security,supermarket automation, interactive product labels, web-browsing fromprinted surfaces, paper based email, and many others.

Using Memjet™ digital printing technology (which is the subject of anumber of pending U.S. patent applications including U.S. Ser. No.10/407,212), Hyperlabel tags are printed over substantially an entiresurface, such as a security document, bank note, or pharmaceuticalpackaging, using infrared (IR) ink. By printing the tags ininfrared-absorptive ink on any substrate which is infrared-reflective,the near-infrared wavelengths, and hence the tags are invisible to thehuman eye but are easily sensed by a solid-state image sensor with anappropriate filter. This allows machine readable information to beencoded over a large portion of the note or other surface, with novisible effect on the original note text or graphics thereon. A scanninglaser or image sensor can read the tags on any part of the surface toperforms associated actions, such as validating each individual note oritem.

An example of such a Hyperlabel encoded document, is shown in FIG. 1. Inthis example, the Hyperlabel document consists of graphic data 2 printedusing visible ink, and coded data 3 formed from Hyperlabel tags 4. Thedocument includes an interactive element 6 defined by a zone 7 whichcorresponds to the spatial extent of a corresponding graphic 8. In use,the tags encode tag data including an ID. By sensing at least one tag,and determining and interpreting the encoded ID using an appropriatesystem, this allows the associated actions to be performed.

In one example, a tag map is used to define a layout of the tags on theHyperlabel document based on the ID encoded within the tag data. The IDcan also be used to reference a document description which describes theindividual elements of the Hyperlabel document, and in particulardescribes the type and spatial extent (zone) of interactive elements,such as a button or text field. Thus, in this example, the element 6 hasa zone 7 which corresponds to the spatial extent of a correspondinggraphic 8. This allows a computer system to interpret interactions withthe Hyperlabel document.

In position indicating techniques, the ID encoded within the tag data ofeach tag allows the exact position of the tag on the Hyperlabel documentto be determined from the tag map. The position can then be used todetermine whether the sensed tag is positioned in a zone of aninteractive element from the document description.

In object indicating techniques, the ID encoded within the tag dataallows the presence of the tag in a region of the document to bedetermined from the tag map (the relative position of the tag within theregion may also be indicated). In this case, the document descriptioncan be used to determine whether the region corresponds to the zone ofan interactive element.

An example of this process will now be described with reference to FIGS.2 and 3 which show how a sensing device in the form of a netpage orNetpage pen 101, which interacts with the coded data on a printedHyperlabel document 1, such as a security document, label, productpackaging or the like.

The Netpage pen 101 senses a tag using an area image sensor and detectstag data. The Netpage pen 101 uses the sensed data tag to generateinteraction data which is transmitted via a short-range radio link 9 toa relay 44, which may form part of a computer 75 or a printer 601. Therelay sends the interaction data, via a network 19, to a document server10, which uses the ID to access the document description, and interpretthe interaction. In appropriate circumstances, the document server sendsa corresponding message to an application server 13, which can thenperform a corresponding action.

In an alternative embodiment, the PC, Web terminal, netpage printer orrelay device may communicate directly with local or remote applicationsoftware, including a local or remote Web server. Relatedly, output isnot limited to being printed by the netpage printer. It can also bedisplayed on the PC or Web terminal, and further interaction can bescreen-based rather than paper-based, or a mixture of the two.

Typically Netpage pen users register with a registration server 11,which associates the user with an identifier stored in the respectiveNetpage pen. By providing the sensing device identifier as part of theinteraction data, this allows users to be identified, allowingtransactions or the like to be performed.

Hyperlabel documents are generated by having an ID server generate an IDwhich is transferred to the document server 10. The document server 10determines a document description and then records an associationbetween the document description and the ID, to allow subsequentretrieval of the document description using the ID.

The ID is then used to generate the tag data, as will be described inmore detail below, before the document is printed by the Hyperlabelprinter 601, using the page description and the tag map.

Each tag is represented by a pattern which contains two kinds ofelements. The first kind of element is a target. Targets allow a tag tobe located in an image of a coded surface, and allow the perspectivedistortion of the tag to be inferred. The second kind of element is amacrodot. Each macrodot encodes the value of a bit by its presence orabsence.

The pattern is represented on the coded surface in such a way as toallow it to be acquired by an optical imaging system, and in particularby an optical system with a narrowband response in the near-infrared.The pattern is typically printed onto the surface using a narrowbandnear-infrared ink.

In the Hyperlabel system the region typically corresponds to the surfaceof an entire product item, or to a security document, and the region IDcorresponds to the unique item ID. For clarity in the followingdiscussion we refer to items and item IDs (or simply IDs), with theunderstanding that the item ID corresponds to the region ID.

The surface coding is designed so that an acquisition field of viewlarge enough to guarantee acquisition of an entire tag is large enoughto guarantee acquisition of the ID of the region containing the tag.Acquisition of the tag itself guarantees acquisition of the tag'stwo-dimensional position within the region, as well as othertag-specific data. The surface coding therefore allows a sensing deviceto acquire a region ID and a tag position during a purely localinteraction with a coded surface, e.g. during a “click” or tap on acoded surface with a pen.

A wide range of different tag structures can be used, and some exampleswill now be described.

First Example Tag Structure

FIG. 4 shows the structure of a complete tag. Each of the four blackcircles is a target. The tag, and the overall pattern, has four-foldrotational symmetry at the physical level.

Each square region represents a symbol, and each symbol represents fourbits of information.

FIG. 5 shows the structure of a symbol. It contains four macrodots, eachof which represents the value of one bit by its presence (one) orabsence (zero).

The macrodot spacing is specified by the parameter s throughout thisdocument. It has a nominal value of 143 μm, based on 9 dots printed at apitch of 1600 dots per inch. However, it is allowed to vary by ±10%according to the capabilities of the device used to produce the pattern.

FIG. 6 shows an array of nine adjacent symbols. The macrodot spacing isuniform both within and between symbols.

FIG. 7 shows the ordering of the bits within a symbol. Bit zero is theleast significant within a symbol; bit three is the most significant.Note that this ordering is relative to the orientation of the symbol.The orientation of a particular symbol within the tag is indicated bythe orientation of the label of the symbol in the tag diagrams. Ingeneral, the orientation of all symbols within a particular segment ofthe tag have the same orientation, consistent with the bottom of thesymbol being closest to the centre of the tag.

Only the macrodots are part of the representation of a symbol in thepattern. The square outline of a symbol is used in this document to moreclearly elucidate the structure of a tag. FIG. 8, by way ofillustration, shows the actual pattern of a tag with every bit set. Notethat, in practice, every bit of a tag can never be set.

A macrodot is nominally circular with a nominal diameter of (5/9)s.However, it is allowed to vary in size by ±10% according to thecapabilities of the device used to produce the pattern.

A target is nominally circular with a nominal diameter of (17/9)s.However, it is allowed to vary in size by ±10% according to thecapabilities of the device used to produce the pattern.

The tag pattern is allowed to vary in scale by up to ±10% according tothe capabilities of the device used to produce the pattern. Anydeviation from the nominal scale is recorded in the tag data to allowaccurate generation of position samples.

Each symbol shown in the tag structure in FIG. 4 has a unique label.Each label consists an alphabetic prefix and a numeric suffix.

Tag Group

Tags are arranged into tag groups. Each tag group contains four tagsarranged in a square. Each tag therefore has one of four possible tagtypes according to its location within the tag group square. The tagtypes are labelled 00, 10, 01 and 11, as shown in FIG. 9.

FIG. 10 shows how tag groups are repeated in a continuous tiling oftags. The tiling guarantees the any set of four adjacent tags containsone tag of each type.

Codewords

The tag contains four complete codewords. Each codeword is of apunctured 2⁴-ary (8,5) Reed-Solomon code.

Two of the codewords are unique to the tag. These are referred to aslocal and are labelled A and B. The tag therefore encodes up to 40 bitsof information unique to the tag.

The remaining two codewords are unique to a tag type, but common to alltags of the same type within a contiguous tiling of tags. These arereferred to as global and are labelled C and D, subscripted by tag type.A tag group therefore encodes up to 160 bits of information common toall tag groups within a contiguous tiling of tags.

The layout of the four codewords is shown in FIG. 11.

Reed-Solomon Encoding

Codewords are encoded using a punctured 2⁴-ary (8,5) Reed-Solomon code.

A 2⁴-ary (8,5) Reed-Solomon code encodes 20 data bits (i.e. five 4-bitsymbols) and 12 redundancy bits (i.e. three 4-bit symbols) in eachcodeword. Its error-detecting capacity is three symbols. Itserror-correcting capacity is one symbol.

As shown in FIG. 12, codeword coordinates are indexed in coefficientorder, and the data bit ordering follows the codeword bit ordering.

A punctured 2⁴-ary (8,5) Reed-Solomon code is a 2⁴-ary (15,5)Reed-Solomon code with seven redundancy coordinates removed. The removedcoordinates are the most significant redundancy coordinates.

The code has the following primitive polynominal:

p(x)=x ⁴ +x+1

The code has the following generator polynominal:

g(x)=(x+α)(x+α ²) . . . (x+α ¹⁰)

For a detailed description of Reed-Solomon codes, refer to Wicker, S. B.and V. K. Bhargava, eds., Reed-Solomon Codes and Their Applications,IEEE Press, 1994.

Tag Coordinate Space

The tag coordinate space has two orthogonal axes labelled x and yrespectively. When the positive x axis points to the right then thepositive y axis points down.

The surface coding does not specify the location of the tag coordinatespace origin on a particular tagged surface, nor the orientation of thetag coordinate space with respect to the surface. This information isapplication-specific. For example, if the tagged surface is a sheet ofpaper, then the application which prints the tags onto the paper mayrecord the actual offset and orientation, and these can be used tonormalise any digital ink subsequently captured in conjunction with thesurface.

The position encoded in a tag is defined in units of tags. Byconvention, the position is taken to be the position of the centre ofthe target closest to the origin.

Tag Information Content

Table 1 defines the information fields embedded in the surface coding.Table 2 defines how these fields map to codewords.

TABLE 1 Field definitions Field width description per codeword codewordtype 2 The type of the codeword, i.e. one of A (b′00′), B (b′01′), C(b′10′) and D (b′11′). per tag tag type 2 The type of the tag, i.e. oneof 00 (b′00′), 01 (b′01′), 10 (b′10′) and 11 (b′11′) - corresponds tothe bottom two bits of the x and y coordinates of the tag. x coordinate13 The unsigned x coordinate of the tag allows a maximum coordinatevalue of approximately 14 m. y coordinate 13 The unsigned y coordinateof the tag^(b). active area flag 1 A flag indicating whether the tag isa member of an active area. b′1′ indicates membership. active area map 1A flag indicating whether an active area map is flag present. b′1′indicates the presence of a map (see next field). If the map is absentthen the value of each map entry is derived from the active area flag(see previous field). active area map 8 A map¹of which of the tag'simmediate eight neighbours are members of an active area. b′1′ indicatesmembership (FIG. 13 indicates the bit ordering of the map) data fragment8 A fragment of an embedded data stream. Only present if the active areamap is absent. per tag group encoding 8 The format of the encoding.format 0: the present encoding Other values are TBA. Region flags 8Flags controlling the interpretation and routing of region-relatedinformation. 0: region ID is an EPC 1: region is linked 2: region isinteractive 3: region is signed 4: region includes data 5: regionrelates to mobile application Other bits are reserved and must be zero.tag size 16 The difference between the actual tag size and adjustmentthe nominal tag size (1.7145 mm (based on 1600 dpi, 9 dots per macrodot,and 12 macrodots per tag)), in 10 nm units, in sign-magnitude format.Region ID 96 The ID of the region containing the tags. CRC 16 A CRC oftag group data (CCITT CRC-16 (ITU, Interface between Data TerminalEquipment (DTE) and Data Circuit-terminating Equipment (DCE) forterminals operating in the packet mode and connected to public datanetworks by dedicated circuit, ITU-T X.25 (10/96)) Total 320

The active area map indicates whether the corresponding tags are membersof an active area. An active area is an area within which any capturedinput should be immediately forwarded to the corresponding Hyperlabelserver for interpretation. It also allows the Hyperlabel sensing deviceto signal to the user that the input will have an immediate effect.

TABLE 2 Mapping of fields to codewords codeword field codeword bitsfield Width bits A 1:0 codeword type 2 all (b′00′) 10:2  x coordinate 912:4  19:11 Y coordinate 9 12:4  B 1:0 codeword type 2 all (b′01′)  2tag type 1 0 5:2 x coordinate 4 3:0  6 tag type 1 1 9:6 y coordinate 43:0 10 active area flag 1 all 11 active area map flag 1 all 19:12 activearea map 8 all 19:12 data fragment 8 all C₀₀ 1:0 codeword type 2 all(b′10′) 9:2 encoding format 8 all 17:10 region flags 8 all 19:18 tagsize adjustment 2 1:0 C₀₁ 1:0 codeword type 2 all (b′10′) 15:2  tag sizeadjustment 14 15:2  19:16 region ID 4 3:0 C₁₀ 1:0 codeword type 2 all(b′10′) 19:2  region ID 18 21:4  C₁₁ 1:0 codeword type 2 all (b′10′)19:2  region ID 18 39:22 D₀₀ 1:0 codeword type 2 all (b′11′) 19:2 region ID 18 57:40 D₀₁ 1:0 codeword type 2 all (b′11′) 19:2  region ID18 75:58 D₁₀ 1:0 codeword type 2 all (b′11′) 19:2  region ID 18 93:76D₁₁ 1:0 codeword type 2 all (b′11′) 3:2 region ID 2 95:94 19:4  CRC 16all

Note that the tag type can be moved into a global codeword to maximiselocal codeword utilization. This in turn can allow larger coordinatesand/or 16-bit data fragments (potentially configurably in conjunctionwith coordinate precision). However, this reduces the independence ofposition decoding from region ID decoding and has not been included inthe specification at this time.

Embedded Data

If the “region includes data” flag in the region flags is set then thesurface coding contains embedded data. The data is encoded in multiplecontiguous tags' data fragments, and is replicated in the surface codingas many times as it will fit.

The embedded data is encoded in such a way that a random and partialscan of the surface coding containing the embedded data can besufficient to retrieve the entire data. The scanning system reassemblesthe data from retrieved fragments, and reports to the user whensufficient fragments have been retrieved without error.

As shown in Table 3, a 200-bit data block encodes 160 bits of data. Theblock data is encoded in the data fragments of A contiguous group of 25tags arranged in a 5×5 square. A tag belongs to a block whose integercoordinate is the tag's coordinate divided by 5. Within each block thedata is arranged into tags with increasing x coordinate withinincreasing y coordinate.

A data fragment may be missing from a block where an active area map ispresent. However, the missing data fragment is likely to be recoverablefrom another copy of the block.

Data of arbitrary size is encoded into a superblock consisting of acontiguous set of blocks arranged in a rectangle. The size of thesuperblock is encoded in each block. A block belongs to a superblockwhose integer coordinate is the block's coordinate divided by thesuperblock size. Within each superblock the data is arranged into blockswith increasing x coordinate within increasing y coordinate.

The superblock is replicated in the surface coding as many times as itwill fit, including partially along the edges of the surface coding.

The data encoded in the superblock may include more precise typeinformation, more precise size information, and more extensive errordetection and/or correction data.

TABLE 3 Embedded data block field width description data type 8 The typeof the data in the superblock. Values include: 0: type is controlled byregion flags 1: MIME Other values are TBA. superblock width 8 The widthof the superblock, in blocks. superblock height 8 The height of thesuperblock, in blocks. data 160 The block data. CRC 16 A CRC of theblock data. total 200

Alternative First Example Tag Structure Tag Group

Tags are arranged into tag groups. Each tag group contains four tagsarranged in a square. Each tag therefore has one of four possible tagtypes according to its location within the tag group square. The tagtypes are labelled 00, 10, 01 and 11, as shown in FIG. 14.

Each tag in the tag group is rotated as shown in the figure, i.e. tagtype 00 is rotated 0 degrees, tag type 10 is rotated 90 degrees, tagtype 11 is rotated 180 degrees, and tag type 01 is rotated 270 degrees.

FIG. 15 shows how tag groups are repeated in a continuous tiling oftags. The tiling guarantees the any set of four adjacent tags containsone tag of each type.

Orientation-Indicating Cyclic Position Code

The tag contains a 2⁴-ary (4, 1) cyclic position codeword which can bedecoded at any of the four possible orientations of the tag to determinethe actual orientation of the tag. Symbols which are part of the cyclicposition codeword have a prefix of “R” and are numbered 0 to 3 in orderof increasing significance.

The cyclic position codeword is (0, 7, 9, E₁₆) Note that it only usesfour distinct symbol values, even though a four-bit symbol has sixteenpossible values. During decoding, any unused symbol value should, ifdetected, be treated as an erasure. To maximise the probability oflow-weight bit error patterns causing erasures rather than symbolerrors, the symbol values are chosen to be as evenly spaced on thehypercube as possible.

The minimum distance of the cyclic position code is 4, hence itserror-correcting capacity is one symbol in the presence of up to oneerasure, and no symbols in the presence of two or more erasures.

The layout of the orientation-indicating cyclic position codeword isshown in FIG. 16.

Local Codeword

The tag locally contains one complete codeword which is used to encodeinformation unique to the tag. The codeword is of a punctured 2⁴-ary(13, 7) Reed-Solomon code. The tag therefore encodes up to 28 bits ofinformation unique to the tag.

The layout of the local codeword is shown in FIG. 17.

Distributed Codewords

The tag also contains fragments of four codewords which are distributedacross the four adjacent tags in a tag group and which are used toencode information common to a set of contiguous tags. Each codeword isof a 2⁴-ary (15,11) Reed-Solomon code. Any four adjacent tags thereforetogether encode up to 176 bits of information common to a set ofcontiguous tags.

The layout of the four complete codewords, distributed across the fouradjacent tags in a tag group, is shown in FIG. 18. The order of the fourtags in the tag group in FIG. 18 is the order of the four tags in FIG.14.

FIG. 19 shows the layout of a complete tag group.

Reed-Solomon Encoding—Local Codeword

The local codeword is encoded using a punctured 2⁴-ary (13, 7)Reed-Solomon code. The code encodes 28 data bits (i.e. seven symbols)and 24 redundancy bits (i.e. six symbols) in each codeword. Itserror-detecting capacity is six symbols. Its error-correcting capacityis three symbols.

As shown in FIG. 20, codeword coordinates are indexed in coefficientorder, and the data bit ordering follows the codeword bit ordering.

The code is a 2⁴-ary (15, 7) Reed-Solomon code with two redundancycoordinates removed. The removed coordinates are the most significantredundancy coordinates.

The code has the following primitive polynominal:

p(x)=x ⁴ +x+1  (EQ 1)

The Code has the Following Generator Polynominal:

g(x)=(x+α)(x+α ²) . . . (x+α ⁸)  (EQ 2)

Reed-Solomon Encoding—Distributed Codewords

The distributed codewords are encoded using a 2⁴-ary (15, 11)Reed-Solomon code. The code encodes 44 data bits (i.e. eleven symbols)and 16 redundancy bits (i.e. four symbols) in each codeword. Itserror-detecting capacity is four symbols. Its error-correcting capacityis two symbols.

Codeword coordinates are indexed in coefficient order, and the data bitordering follows the codeword bit ordering.

The code has the same primitive polynominal as the local codeword code.

The code has the following generator polynominal:

g(x)=(x+α)(x+α ²) . . . (x+α ⁴)  (EQ 3)

Tag Coordinate Space

The tag coordinate space has two orthogonal axes labelled x and yrespectively. When the positive x axis points to the right then thepositive y axis points down.

The surface coding does not specify the location of the tag coordinatespace origin on a particular tagged surface, nor the orientation of thetag coordinate space with respect to the surface. This information isapplication-specific. For example, if the tagged surface is a sheet ofpaper, then the application which prints the tags onto the paper mayrecord the actual offset and orientation, and these can be used tonormalise any digital ink subsequently captured in conjunction with thesurface.

The position encoded in a tag is defined in units of tags. Byconvention, the position is taken to be the position of the centre ofthe target closest to the origin.

Tag Information Content Field Definitions

Table 4 defines the information fields embedded in the surface coding.Table 5 defines how these fields map to codewords.

TABLE 4 Field definitions width field (bits) description per tag xcoordinate 9 or 13 The unsigned x coordinate of the tag allows maximumcoordinate values of approximately 0.9 m and 14 m respectively. ycoordinate 9 or 13 The unsigned y coordinate of the tag allows maximumcoordinate values of approximately 0.9 m and 14 m respectively activearea flag 1 A flag indicating whether the area (the diameter of thearea, centered on the tag, is nominally 5 times the diagonal size of thetag) immediately surrounding the tag intersects an active area. b′1′indicates intersection. data fragment flag 1 A flag indicating whether adata fragment is present (see next field). b′1′ indicates the presenceof a data fragment. If the data fragment is present then the width ofthe x and y coordinate fields is 9. If it is absent then the width is13. data fragment 0 or 8 A fragment of an embedded data stream. per taggroup (i.e. per region) encoding format 8 The format of the encoding. 0:the present encoding Other values are reserved. region flags 8 Flagscontrolling the interpretation of region data. 0: region ID is an EPC 1:region has signature 2: region has embedded data 3: embedded data issignature Other bits are reserved and must be zero. tag size ID 8 The IDof the tag size. 0: the present tag size the nominal tag size is 1.7145mm, based on 1600 dpi, 9 dots per macrodot, and 12 macrodots per tagOther values are reserved. region ID 96  The ID of the region containingthe tags. signature 36  The signature of the region. high-order 4 Thewidth of the high-order part of the x and coordinate width y coordinatesof the tag. (w) high-order x 0 to 15 High-order part of the x coordinateof the coordinate tag expands the maximum coordinate values toapproximately 2.4 km and 38 km respectively high-order y 0 to 15High-order part of the y coordinate of the coordinate tag expands themaximum coordinate values to approximately 2.4 km and 38 kmrespectively. CRC 16  A CRC of tag group data.

An active area is an area within which any captured input should beimmediately forwarded to the corresponding Hyperlabel server forinterpretation. This also allows the Hyperlabel server to signal to theuser that the input has had an immediate effect. Since the server hasaccess to precise region definitions, any active area indication in thesurface coding can be imprecise so long as it is inclusive.

The width of the high-order coordinate fields, if non-zero, reduces thewidth of the signature field by a corresponding number of bits. Fullcoordinates are computed by prepending each high-order coordinate fieldto its corresponding coordinate field.

TABLE 5 Mapping of fields to codewords codeword field codeword bitsfield width bits A 12:0  x coordinate 13 all 12:9  data fragment 4 3:025:13 y coordinate 13 all 25:22 data fragment 4 7:4 26 active area flag1 all 27 data fragment flag 1 all B 7:0 encoding format 8 all 15:8 region flags 8 all 23:16 tag size ID 8 all 39:24 CRC 16 all 43:40high-order 4 3:0 coordinate width (w) C 35:0  signature 36 all (35 −w):(36 − high-order x w all 2w) coordinate 35:(36 − w) high-order y wall coordinate 43:36 region ID 8 7:0 D 43:0  region ID 44 51:8  E 43:0 region ID 44 95:52

Embedded Data

If the “region has embedded data” flag in the region flags is set thenthe surface coding contains embedded data. The data is encoded inmultiple contiguous tags' data fragments, and is replicated in thesurface coding as many times as it will fit.

The embedded data is encoded in such a way that a random and partialscan of the surface coding containing the embedded data can besufficient to retrieve the entire data. The scanning system reassemblesthe data from retrieved fragments, and reports to the user whensufficient fragments have been retrieved without error.

As shown in Table 6, a 200-bit data block encodes 160 bits of data. Theblock data is encoded in the data fragments of a contiguous group of 25tags arranged in a 5×5 square. A tag belongs to a block whose integercoordinate is the tag's coordinate divided by 5. Within each block thedata is arranged into tags with increasing x coordinate withinincreasing y coordinate.

A data fragment may be missing from a block where an active area map ispresent. However, the missing data fragment is likely to be recoverablefrom another copy of the block.

Data of arbitrary size is encoded into a superblock consisting of acontiguous set of blocks arranged in a rectangle. The size of thesuperblock is encoded in each block. A block belongs to a superblockwhose integer coordinate is the block's coordinate divided by thesuperblock size. Within each superblock the data is arranged into blockswith increasing x coordinate within increasing y coordinate.

The superblock is replicated in the surface coding as many times as itwill fit, including partially along the edges of the surface coding.

The data encoded in the superblock may include more precise typeinformation, more precise size information, and more extensive errordetection and/or correction data.

TABLE 6 Embedded data block field width description data type 8 The typeof the data in the superblock. Values include: 0: type is controlled byregion flags 1: MIME Other values are TBA. superblock width 8 The widthof the superblock, in blocks. superblock height 8 The height of thesuperblock, in blocks. data 160 The block data. CRC 16 A CRC of theblock data. total 200

It will be appreciated that any form of embedded data may be used,including for example, text, image, audio, video data, such as productinformation, application data, contact data, business card data, anddirectory data.

Region Signatures

If the “region has signature” flag in the region flags is set then thesignature field contains a signature with a maximum width of 36 bits.The signature is typically a random number associated with the region IDin a secure database. The signature is ideally generated using a trulyrandom process, such as a quantum process, or by distilling randomnessfrom random events.

In an online environment the signature can be validated, in conjunctionwith the region ID, by querying a server with access to the securedatabase.

If the “region has embedded data” and “embedded data is signature” flagsin the region flags are set then the surface coding contains a 160-bitcryptographic signature of the region ID. The signature is encoded in aone-block superblock.

In an online environment any number of signature fragments can be used,in conjunction with the region ID and optionally the random signature,to validate the signature by querying a server with knowledge of thefull signature or the corresponding private key.

In an offline (or online) environment the entire signature can berecovered by reading multiple tags, and can then be validated using thecorresponding public signature key.

Signature verification is discussed in more detail below.

Second Example Tag Structure

FIG. 21 shows the structure of a complete tag. Each of the six blackcircles is a target. The tag, and the overall pattern, has six-foldrotational symmetry at the physical level.

Each diamond-shaped region represents a symbol, and each symbolrepresents four bits of information.

FIG. 22 shows the structure of a symbol. It contains four macrodots,each of which represents the value of one bit by its presence (one) orabsence (zero).

The macrodot spacing is specified by the parameter s throughout thisdocument. It has a nominal value of 143 μm, based on 9 dots printed at apitch of 1600 dots per inch. However, it is allowed to vary by ±10%according to the capabilities of the device used to produce the pattern.

FIG. 23 shows an array of five adjacent symbols. The macrodot spacing isuniform both within and between symbols.

FIG. 24 shows the ordering of the bits within a symbol. Bit zero is theleast significant within a symbol; bit three is the most significant.Note that this ordering is relative to the orientation of the symbol.The orientation of a particular symbol within the tag is indicated bythe orientation of the label of the symbol in the tag diagrams. Ingeneral, the orientation of all symbols within a particular segment ofthe tag have the same orientation, consistent with the bottom of thesymbol being closest to the centre of the tag.

Only the macrodots are part of the representation of a symbol in thepattern. The diamond-shaped outline of a symbol is used in this documentto more clearly elucidate the structure of a tag. FIG. 25, by way ofillustration, shows the actual pattern of a tag with every bit set. Notethat, in practice, every bit of a tag can never be set.

A macrodot is nominally circular with a nominal diameter of (5/9)s.However, it is allowed to vary in size by ±10% according to thecapabilities of the device used to produce the pattern.

A target is nominally circular with a nominal diameter of (17/9)s.However, it is allowed to vary in size by ±10% according to thecapabilities of the device used to produce the pattern.

The tag pattern is allowed to vary in scale by up to ±10% according tothe capabilities of the device used to produce the pattern. Anydeviation from the nominal scale is recorded in the tag data to allowaccurate generation of position samples.

Each symbol shown in the tag structure in FIG. 21 has a unique label.Each label consists an alphabetic prefix and a numeric suffix.

Tag Group

Tags are arranged into tag groups. Each tag group contains three tagsarranged in a line. Each tag therefore has one of three possible tagtypes according to its location within the tag group. The tag types arelabelled P, Q and R, as shown in FIG. 26.

FIG. 27 shows how tag groups are repeated in a continuous tiling oftags. The tiling guarantees the any set of three adjacent tags containsone tag of each type.

Orientation-Indicating Cyclic Position Code

The tag contains a 2³-ary (6,1) cyclic position codeword (this work iscurrently the subject of two pending US Patent applications, entitled“Cyclic position codes” and “Orientation indicating cyclic positioncodes” with application Ser. Nos. 10/120,441 and 10/409,864,respectively) which can be decoded at any of the six possibleorientations of the tag to determine the actual orientation of the tag.Symbols which are part of the cyclic position codeword have a prefix of“R” and are numbered 0 to 5 in order of increasing significance.

The layout of the orientation-indicating cyclic position codeword isshown in FIG. 28.

The cyclic position codeword is (0, 5, 6, 9, A₁₆, F₁₆). Note that itonly uses six distinct symbol values, even though a four-bit symbol hassixteen possible values. During decoding, any unused symbol valueshould, if detected, be treated as an erasure. To maximise theprobability of low-weight bit error patterns causing erasures ratherthan symbol errors, the symbol values are chosen to be evenly-spaced onthe hypercube.

The minimum distance of the cyclic position code is 6, hence itserror-correcting capacity is two symbols in the presence of up to oneerasure, one symbol in the presence of two or three erasures, and nosymbols in the presence of four or more erasures.

Local Codeword

The tag locally contains one complete codeword, labelled A, which isused to encode information unique to the tag. The codeword is of apunctured 2⁴-ary (12,7) Reed-Solomon code. The tag therefore encodes upto 28 bits of information unique to the tag.

The layout of the local codeword is shown in FIG. 29.

Distributed Codewords

The tag also contains fragments of six codewords, labelled B through G,which are distributed across three adjacent tags and which are used toencode information common to a set of contiguous tags. Each codeword isof a punctured 2⁴-ary (12,7) Reed-Solomon code. Any three adjacent tagstherefore together encode up to 168 bits of information common to a setof contiguous tags.

The layout of the first four fragments of the six codewords B through Gin tag type P is shown in FIG. 30. The layout in the other tag typesfollows the layout in tag type P, with symbols 4 through 7 in tag typeQ, and fragments 8 through 11 in tag type Q.

The layout of the six complete codewords B through G, distributed acrossthe three tag types P, Q and R, is shown in FIG. 31.

As shown earlier in FIG. 27, the tiling guarantees the any set of threeadjacent tags contains one tag of each type, and therefore contains acomplete set of distributed codewords. The tag type, used to determinethe registration of the distributed codewords with respect to aparticular set of adjacent tags, is inferred from the x-y coordinateencoded in the local codeword of each tag.

Tag Segment Geometry

FIG. 32 shows the geometry of a tag segment.

FIG. 33 shows the spacing d between tag segments, required to maintainconsistent spacing between macrodots, where d is given by:

d=(1−√{square root over (3)}/2)s

FIG. 34 shows the effect of the inter-segment spacing d on targetposition. Compared with their nominal positions in relation toclosely-packed segments (i.e. with d=0), diagonal targets must bedisplaced by

(Δ_(x),Δ_(y))=(±1/√{square root over (3)},±1)d

and horizontal targets must be displaced by

(Δ_(x),Δ_(y))=(±2/√{square root over (3)},0)d

Reed-Solomon Encoding

Codewords are encoded using a punctured 2⁴-ary (12,7) Reed-Solomon code.

A 2⁴-ary (12,7) Reed-Solomon code encodes 28 data bits (i.e. seven 4-bitsymbols) and 20 redundancy bits (i.e. five 4-bit symbols) in eachcodeword. Its error-detecting capacity is five symbols. Itserror-correcting capacity is two symbols.

As shown in FIG. 35, codeword coordinates are indexed in coefficientorder, and the data bit ordering follows the codeword bit ordering.

A punctured 2⁴-ary (12,7) Reed-Solomon code is a 2⁴-ary (15,7)Reed-Solomon code with three redundancy coordinates removed. The removedcoordinates are the most significant redundancy coordinates.

The code has the following primitive polynominal:

p(x)=x ⁴ +x+1

The code has the following generator polynominal:

g(x)=(x+α)(x+α ²) . . . (x+α ⁸)

For a detailed description of Reed-Solomon codes, refer to Wicker, S. B.and V. K. Bhargava, eds., Reed-Solomon Codes and Their Applications,IEEE Press, 1994.

Tag Coordinate Space

The tag coordinate space has two orthogonal axes labelled x and yrespectively. When the positive x axis points to the right then thepositive y axis points down.

The surface coding does not specify the location of the tag coordinatespace origin on a particular tagged surface, nor the orientation of thetag coordinate space with respect to the surface. This information isapplication-specific. For example, if the tagged surface is a sheet ofpaper, then the application which prints the tags onto the paper mayrecord the actual offset and orientation, and these can be used tonormalise any digital ink subsequently captured in conjunction with thesurface.

The position encoded in a tag is defined in units of tags. Tagcoordinates are arranged as shown in FIG. 36, where the tag withcoordinate (0,0) is a P type tag. By convention, the position of a tagwith an even y coordinate is defined to be the position of the center ofthe tag. The position of a tag with an odd y coordinate is thereforedefined to be the position of the midpoint between the center of the tagand the center of its neighboring tag on the left.

Horizontal and vertical tag units, based on center-to-center tag tagspacings, are given by:

$u_{x} = {{{4\left( {2\sqrt{3}\mspace{14mu} s} \right)} + {2d}} \cong {14.1\mspace{14mu} s}}$$u_{y} = {{{6\left( {2\mspace{14mu} s} \right)} + {2\left( {d\frac{\sqrt{3}}{2}} \right)}} \cong {12.2\mspace{14mu} s}}$

where d is the inter-segment spacing given by

d=(1−√{square root over (3)}/2)s

If the three tag types P, Q and R are assigned values 0, 1 and 2respectively, then the type^(t) of a tag is inferred from its (x,y)coordinate as follows. If y is even, then:

t=x modulo 3

if y is odd, then:

t=(x−1)modulo 3

Tag Information Content

Table 7 defines the information fields embedded in the surface coding.Table 8 defines how these fields map to codewords.

TABLE 7 Field Definitions field width description per tag X coordinate10 The unsigned x coordinate of the tag allows a maximum x coordinatevalue of approximately 2.1 m (based on EQ 4). Y coordinate 10 Theunsigned y coordinate of the tag allows a maximum y coordinate value ofapproximately 1.8 m (based on EQ 5. active area flag 1 A flag indicatingwhether the tag is a member of an active area. b′1′ indicatesmembership. active area map flag 1 A flag indicating whether an activearea map is present. b′1′ indicates the presence of a map (see nextfield). If the map is absent then the value of each map entry is derivedfrom the active area flag (see previous field). active area map 6 A mapof which of the tag's immediate six neighbours are members of an activearea. b′1′ indicates membership - FIG. 37 indicates the bit ordering ofthe map data fragment 6 A fragment of an embedded data stream. Onlypresent if the active area map is absent. per tag group encoding format12 The format of the encoding. 0: the present encoding Other values areTBA. macrodot spacing 16 The difference between the actual macrodotadjustment spacing and the nominal macrodot spacing, in nm units, insign-magnitude format - the nominal macrodot spacing is 142875 nm (basedon 1600 dpi and 9 dots per macrodot) region flags 12 Flags controllingthe interpretation and routing of region-related information. 0: regionID is an EPC 1: region is linked 2: region is interactive 3: region issigned 4: region includes data 5: region relates to mobile applicationOther bits are reserved and must be zero. region ID 112 The ID of theregion containing the tags. CRC 16 A CRC (CCITT CRC-16) of tag groupdata.

The active area map indicates whether the corresponding tags are membersof an active area. An active area is an area within which any capturedinput should be immediately forwarded to the corresponding Hyperlabelserver for interpretation. It also allows the Hyperlabel sensing deviceto signal to the user that the input will have an immediate effect.

TABLE 8 Mapping of fields to codewords codeword field field codewordbits width bits field A 9:0 10 all x coordinate 19:10 10 all ycoordinate 20 1 all active area flag 21 1 all active area map flag 27:226 all active area map 27:22 6 all data fragment B 11:0  12 all Encodingformat 27:12 16 all Macrodot spacing adjustment C 11:0  12 all regionflags 27:12 16 27:12 region ID D 27:0  28 55:28 E 27:0  28 83:56 F 27:0 28 111:84  G 11:0  12 11:0  27:12 16 all CRC

Embedded Data

If the “region includes data” flag in the region flags is set then thesurface coding contains embedded data. The data is encoded in multiplecontiguous tags' data fragments, and is replicated in the surface codingas many times as it will fit.

The embedded data is encoded in such a way that a random and partialscan of the surface coding containing the embedded data can besufficient to retrieve the entire data. The scanning system reassemblesthe data from retrieved fragments, and reports to the user whensufficient fragments have been retrieved without error.

As shown in Table 9, a 216-bit data block encodes 160 bits of data.

TABLE 9 Embedded data block field width Description data type 16 Thetype of the data in the superblock. Values include: 0: type iscontrolled by region flags 1: MIME Other values are TBA. superblockwidth 12 The width of the superblock, in blocks. superblock height 12The height of the superblock, in blocks. data 160 The block data. CRC 16A CRC of the block data. total 216

The block data is encoded in the data fragments of a contiguous group of36 tags arranged in a 6×6 square as shown in FIG. 38. A tag belongs to ablock whose integer x and y coordinates are the tag's x and ycoordinates divided by 6. Within each block the data is arranged intotags with increasing x coordinate within increasing y coordinate.

A data fragment may be missing from a block where an active area map ispresent. However, the missing data fragment is likely to be recoverablefrom another copy of the block.

Data of arbitrary size is encoded into a superblock consisting of acontiguous set of blocks arranged in a rectangle. The size of thesuperblock is encoded in each block. A block belongs to a superblockwhose integer coordinate is the block's coordinate divided by thesuperblock size. Within each superblock the data is arranged into blockswith increasing x coordinate within increasing y coordinate.

The superblock is replicated in the surface coding as many times as itwill fit, including partially along the edges of the surface coding.

The data encoded in the superblock may include more precise typeinformation, more precise size information, and more extensive errordetection and/or correction data.

General Considerations Cryptographic Signature of Region ID

If the “region is signed” flag in the region flags is set then thesurface coding contains a 160-bit cryptographic signature of the regionID. The signature is encoded in a one-block superblock.

In an online environment any signature fragment can be used, inconjunction with the region ID, to validate the signature. In an offlineenvironment the entire signature can be recovered by reading multipletags, and can then be validated using the corresponding public signaturekey.

MIME Data

If the embedded data type is “MIME” then the superblock containsMultipurpose Internet Mail Extensions (MIME) data according to RFC 2045(Freed, N., and N. Borenstein, “Multipurpose Internet Mail Extensions(MIME)—Part One: Format of Internet Message Bodies”, RFC 2045, November1996), RFC 2046 (Freed, N., and N. Borenstein, “Multipurpose InternetMail Extensions (MIME)—Part Two: Media Types”, RFC 2046, November 1996)and related RFCs. The MIME data consists of a header followed by a body.The header is encoded as a variable-length text string preceded by an8-bit string length. The body is encoded as a variable-lengthtype-specific octet stream preceded by a 16-bit size in big-endianformat.

The basic top-level media types described in RFC 2046 include text,image, audio, video and application.

RFC 2425 (Howes, T., M. Smith and F. Dawson, “A MIME Content-Type forDirectory Information”, RFC 2045, September 1998) and RFC 2426 (Dawson,F., and T. Howes, “vCard MIME Directory Profile”, RFC 2046, September1998) describe a text subtype for directory information suitable, forexample, for encoding contact information which might appear on abusiness card.

Encoding and Printing Considerations

The Print Engine Controller (PEC) (which is the subject of a number ofpending US patent applications, including: Ser. No. 09/575,108; Ser. No.10/727,162; Ser. No. 09/575,110; Ser. No. 09/607,985; U.S. Pat. No.6,398,332; U.S. Pat. No. 6,394,573; U.S. Pat. No. 6,622,923) supportsthe encoding of two fixed (per-page) 2⁴-ary (15,7) Reed-Solomoncodewords and four variable (per-tag) 2⁴-ary (15,7) Reed-Solomoncodewords, although other numbers of codewords can be used for differentschemes.

Furthermore, PEC supports the rendering of tags via a rectangular unitcell whose layout is constant (per page) but whose variable codeworddata may vary from one unit cell to the next. PEC does not allow unitcells to overlap in the direction of page movement.

A unit cell compatible with PEC contains a single tag group consistingof four tags. The tag group contains a single A codeword unique to thetag group but replicated four times within the tag group, and fourunique B codewords. These can be encoded using five of PEC's sixsupported variable codewords. The tag group also contains eight fixed Cand D codewords. One of these can be encoded using the remaining one ofPEC's variable codewords, two more can be encoded using PEC's two fixedcodewords, and the remaining five can be encoded and pre-rendered intothe Tag Format Structure (TFS) supplied to PEC.

PEC imposes a limit of 32 unique bit addresses per TFS row. The contentsof the unit cell respect this limit. PEC also imposes a limit of 384 onthe width of the TFS. The contents of the unit cell respect this limit.

Note that for a reasonable page size, the number of variable coordinatebits in the A codeword is modest, making encoding via a lookup tabletractable. Encoding of the B codeword via a lookup table may also bepossible. Note that since a Reed-Solomon code is systematic, only theredundancy data needs to appear in the lookup table.

Imaging and Decoding Considerations

The minimum imaging field of view required to guarantee acquisition ofan entire tag has a diameter of 39.6s, i.e.

(2×(12+2))√{square root over (2)}s

allowing for arbitrary alignment between the surface coding and thefield of view. Given a macrodot spacing of 143 μm, this gives a requiredfield of view of 5.7 mm.

Table 10 gives pitch ranges achievable for the present surface codingfor different sampling rates, assuming an image sensor size of 128pixels.

TABLE 10 Pitch ranges achievable for present surface coding fordifferent sampling rates, computed using Optimize Hyperlabel Optics; dotpitch = 1600 dpi, macrodot pitch = 9 dots, viewing distance = 30 mm,nib-to-FOV separation = 1 mm, image sensor size = 128 pixels samplingrate pitch range 2 −40 to

 49 2.5 −27 to

 36 3 −10 to

 18

For the surface coding of the first example, the corresponding decodingsequence is as follows:

-   -   locate targets of complete tag    -   infer perspective transform from targets    -   sample and decode any one of tag's four codewords    -   determine codeword type and hence tag orientation    -   sample and decode required local (A and B) codewords    -   codeword redundancy is only 12 bits, so only detect errors    -   on decode error flag bad position sample    -   determine tag x-y location, with reference to tag orientation    -   infer 3D tag transform from oriented targets    -   determine nib x-y location from tag x-y location and 3D        transform    -   determine active area status of nib location with reference to        active area map    -   generate local feedback based on nib active area status    -   determine tag type from A codeword    -   sample and decode required global (C and D) codewords (modulo        window alignment, with reference to tag type)    -   although codeword redundancy is only 12 bits, correct errors;        subsequent CRC verification will detect erroneous error        correction    -   verify tag group data CRC    -   on decode error flag bad region ID sample    -   determine encoding type, and reject unknown encoding    -   determine region flags    -   determine region ID    -   encode region ID, nib x-y location, nib active area status in        digital ink    -   route digital ink based on region flags

Note that region ID decoding need not occur at the same rate as positiondecoding.

Note that decoding of a codeword can be avoided if the codeword is foundto be identical to an already-known good codeword.

For the surface coding of the alternative first example, thecorresponding decoding sequence is as follows:

-   -   locate targets of complete tag    -   infer perspective transform from targets    -   sample cyclic position code    -   decode cyclic position code    -   determine orientation from cyclic position code    -   sample and decode local Reed-Solomon codeword    -   determine tag x-y location    -   infer 3D tag transform from oriented targets    -   determine nib x-y location from tag x-y location and 3D        transform    -   determine active area status of nib location with reference to        active area map    -   generate local feedback based on nib active area status    -   determine tag type    -   sample distributed Reed-Solomon codewords (modulo window        alignment, with reference to tag type)    -   decode distributed Reed-Solomon codewords    -   verify tag group data CRC    -   on decode error flag bad region ID sample    -   determine encoding type, and reject unknown encoding    -   determine region flags    -   determine region ID    -   encode region ID, nib x-y location, nib active area status in        digital ink    -   route digital ink based on region flags

Region ID decoding need not occur at the same rate as position decodingand decoding of a codeword can be avoided if the codeword is found to beidentical to an already-known good codeword.

If the high-order coordinate width is non-zero, then special care mustbe taken on boundaries between tags where the low-order x or ycoordinate wraps, otherwise codeword errors may be introduced. Ifwrapping is detected from the low-order x or y coordinate (i.e. itcontains all zero bits or all one bits), then the correspondinghigh-order coordinate can be adjusted before codeword decoding. In theabsence of genuine symbol errors in the high-order coordinate, this willprevent the inadvertent introduction of codeword errors.

Expanded Tag

The tag can be expanded to increase its data capacity by addingadditional bands of symbols about its circumference. This appendixdescribes an expanded tag with one additional band of symbols. While thetag described in the main part of the document has a raw capacity of 36symbols, the expanded tag has a raw capacity of 60 symbols.

The capacity of the expanded tag is precisely sufficient to allow theinclusion of a complete 160-bit digital signature in each tag group.This allows complete digital signature verification on a “single-click”interaction with the surface coding.

Tag Structure

FIG. 39 shows the structure of a complete (P type) expanded tag. Apartfrom the additional band of symbols and the related change in thepositions of the targets, it has a similar physical structure to the tagdescribed earlier.

In the expanded tag the macrodot spacing ^(s) has a nominal value of 111μm, based on 7 dots printed at a pitch of 1600 dots per inch.

A macrodot is nominally circular with a nominal diameter of (3/7)s.

A target is nominally circular with a nominal diameter of (10/7)s.

The expanded tag, like the tag described earlier, also participates in atag group, and each expanded tag has one of the three possible tag typesP, Q and R.

The expanded tag, like the tag described earlier, contains anorientation-indicating cyclic position code.

Local Codeword

The expanded tag locally contains one complete codeword which is used toencode information unique to the tag. The codeword is of a punctured2⁴-ary (12,7) Reed-Solomon code. The tag therefore encodes up to 28 bitsof information unique to the tag.

The layout of the local codeword is shown in FIG. 40.

Distributed Codewords

The expanded tag contains fragments of twelve codewords, labelled Bthrough M, which are distributed across three adjacent tags and whichare used to encode information common to a set of contiguous tags. Eachcodeword is of a punctured 2⁴-ary (12,7) Reed-Solomon code. Any threeadjacent tags therefore together encode up to 336 bits of informationcommon to a set of contiguous tags.

The layout of the first four fragments of the six codewords B through Gin tag type P is shown in FIG. 41. The layout in the other tag typesfollows the layout in tag type P, with symbols 4 through 7 in tag typeQ, and fragments 8 through 11 in tag type Q.

The layout of the first four fragments of the six codewords H through Min tag type P is shown in FIG. 42. The layout in the other tag typesfollows the layout in tag type P, with symbols 4 through 7 in tag typeQ, and fragments 8 through 11 in tag type Q.

As shown earlier in FIG. 37, the tiling guarantees the any set of threeadjacent tags contains one tag of each type, and therefore contains acomplete set of distributed codewords. The tag type, used to determinethe registration of the distributed codewords with respect to aparticular set of adjacent tags, is inferred from the x-y coordinateencoded in the local codeword of each tag.

Tag Coordinate Space

The tag coordinate space encoded in the expanded tag is identical tothat encoded in the tag described earlier, with the exception that tagunits are different (due both to the change in tag structure and thechange in macrodot spacing).

Horizontal and vertical tag units, based on center-to-center tag tagspacings, are given by:

$u_{x} = {{{5\left( {2\sqrt{3}\mspace{14mu} s} \right)} + {2d}} \cong {17.6\mspace{14mu} s}}$$u_{y} = {{{7.5\left( {2\mspace{14mu} s} \right)} + {2\left( {d\frac{\sqrt{3}}{2}} \right)}} \cong {15.2\mspace{14mu} s}}$

where d is the inter-segment spacing given by

d=(1−√{square root over (3)}/2)s

Tag Information Content

Table 11 defines the information fields embedded in the expanded tagsurface coding. Table 12 defines how these fields map to codewords.

TABLE 11 Field definitions Field width description per tag x coordinate10 The unsigned x coordinate of the tag - allows a maximum x coordinatevalue of approximately 2.0 m (based on EQ 8). y coordinate 10 Theunsigned y coordinate of the tag - allows a maximum y coordinate valueof approximately 1.7 m (based on EQ 9) active area flag 1 A flagindicating whether the tag is a member of an active area. b′1′ indicatesmembership. active area map 1 A flag indicating whether an active areamap is flag present. b′1′ indicates the presence of a map (see nextfield). If the map is absent then the value of each map entry is derivedfrom the active area flag (see previous field). active area map 6 A mapof which of the tag's immediate six neighbours are members of an activearea. b′1′ indicates membership - FIG. 37 indicates the bit ordering ofthe map data fragment 6 A fragment of an embedded data stream. Onlypresent if the active area map is absent. per tag group encoding 12 Theformat of the encoding. format Refer to Table 5 for values. macrodot 16The difference between the actual macrodot spacing spacing and thenominal macrodot spacing, in adjustment nm units, in sign-magnitudeformat - the nominal macrodot spacing is 111125 nm (based on 1600 dpiand 7 dots per macrodot region flags 12 Flags controlling theinterpretation and routing of region-related information. Refer to Table5 for values. region ID 112 The ID of the region containing the tags.Signature 160 A digital signature of the region ID. CRC 16 A CRC (CCITTCRC-16) of tag group data.

TABLE 12 Mapping of fields to codewords codeword field field codewordbits width bits field A  9:0 10 all x coordinate  19:10 10 all ycoordinate 20 1 all active area flag 21 1 all active area map flag 27:22 6 all active area map  27:22 6 all data fragment B 11:0 12 allencoding format  27:12 16 all macrodot spacing adjustment C 11:0 12 allregion flags  27:12 16 27:12 region ID D 27:0 28 55:28 E 27:0 28 83:56 F27:0 28 111:84  G 11:0 12 11:0   27:12 16 all CRC H 27:0 28 27:0 signature I 27:0 28 55:28 J 27:0 28 83:56 K 27:0 28 111:84  L 27:0 28139:112 M 19:0 20 159:140  27:20 8 all unused

Encoding and Printing Considerations

The tag group unit cell of the expanded tag only respects PEC's TFSwidth limit if the macrodot spacing is reduced from 9 to 7 dots, asreflected in the macrodot spacing ^(s) of 111 μm.

Imaging and Decoding Considerations

The minimum imaging field of view required to guarantee acquisition ofan entire expanded tag has a diameter of 44s i.e.

2(1+8+2)2s),

allowing for arbitrary alignment between the surface coding and thefield of view. Given a macrodot spacing of 111 μm this gives a requiredfield of view of approximately 4.0 mm.

Surface Coding Security Security Requirements

Item security can be defined to have two related purposes:

-   -   to allow authentication of an item    -   to prevent forgery of an item

The greater the difficulty of forgery, the greater the trustworthinessof authentication. When an item is coded, Hyperlabel surface codingsecurity has two corresponding purposes:

-   -   to allow authentication of a coded item    -   to prevent forgery of a coded item with a novel item ID

If a user is able to determine the authenticity of the surface coding ofan item, then the user may be able to make an informed decision aboutthe likely authenticity of the item.

If it is intractable to forge the surface coding for a novel ID, thenthe only tractable way of forging an item with an authentic surfacecoding is to duplicate the surface coding of an existing item (and henceits ID). If the user is able to determine by other means that the ID ofan item is likely to be unique, then the user may assume that the itemis authentic.

Since the Hyperlabel surface coding allows meaningful interactionbetween a sensing device and a coded surface during a purely localinteraction, it is desirable for the surface coding to supportauthentication during a similarly local interaction, i.e. withoutrequiring an increase in the size of the sensing device field of view.

Since no a priori relationship exists between creators of authenticcoded items and users potentially wishing to authenticate such items, itis undesirable to require a trust relationship between creators andusers. For example, it is undesirable to require that creators sharesecret signature keys with users.

It is reasonable for many users to rely on online access to anauthenticator trusted by a creator for the purposes of authenticatingitems. Conversely, it is desirable to allow authentication to take placein the absence of online access.

Security Discussion

As described above, authentication relies on verifying thecorrespondence between data and a signature of that data. The greaterthe difficulty in forging a signature, the greater the trustworthinessof signature-based authentication.

The item ID is unique and therefore provides a basis for a signature. Ifonline authentication access is assumed, then the signature may simplybe a random number associated with the item ID in an authenticationdatabase accessible to the trusted online authenticator. The randomnumber may be generated by any suitable method, such as via adeterministic (pseudo-random) algorithm, or via a stochastic physicalprocess. A keyed hash or encrypted hash may be preferable to a randomnumber since it requires no additional space in the authenticationdatabase. However, a random signature of the same length as a keyedsignature is more secure than the keyed signature since it is notsusceptible to key attacks. Equivalently, a shorter random signatureconfers the same security as a longer keyed signature.

In the limit case no signature is actually required, since the merepresence of the item ID in the database indicates authenticity. However,the use of a signature limits a forger to forging items he has actuallysighted.

To prevent forgery of a signature for an unsighted ID, the signaturemust be large enough to make exhaustive search via repeated accesses tothe online authenticator intractable. If the signature is generatedusing a key rather than randomly, then its length must also be largeenough to prevent the forger from deducing the key from knownID-signature pairs. Signatures of a few hundred bits are consideredsecure, whether generated using private or secret keys.

While it may be practical to include a reasonably secure randomsignature in a tag (or local tag group), particularly if the length ofthe ID is reduced to provide more space for the signature, it may beimpractical to include a secure ID-derived signature in a tag. Tosupport a secure ID-derived signature, we can instead distributefragments of the signature across multiple tags. If each fragment can beverified in isolation against the ID, then the goal of supportingauthentication without increasing the sensing device field of view isachieved. The security of the signature can still derive from the fulllength of the signature rather than from the length of a fragment, sincea forger cannot predict which fragment a user will randomly choose toverify. A trusted authenticator can always perform fragment verificationsince they have access to the key and/or the full stored signature, sofragment verification is always possible when online access to a trustedauthenticator is available.

Fragment verification requires that we prevent brute force attacks onindividual fragments, otherwise a forger can determine the entiresignature by attacking each fragment in turn. A brute force attack canbe prevented by throttling the authenticator on a per-ID basis. However,if fragments are short, then extreme throttling is required. As analternative to throttling the authenticator, the authenticator caninstead enforce a limit on the number of verification requests it iswilling to respond to for a given fragment number. Even if the limit ismade quite small, it is unlikely that a normal user will exhaust it fora given fragment, since there will be many fragments available and theactual fragment chosen by the user can vary. Even a limit of one can bepractical. More generally, the limit should be proportional to the sizeof the fragment, i.e. the smaller the fragment the smaller the limit.Thus the experience of the user would be somewhat invariant of fragmentsize. Both throttling and enforcing fragment verification limits implyserialisation of requests to the authenticator. A fragment verificationlimit need only be imposed once verification fails, i.e. an unlimitednumber of successful verifications can occur before the first failure.Enforcing fragment verification limits further requires theauthenticator to maintain a per-fragment count of satisfied verificationrequests.

A brute force attack can also be prevented by concatenating the fragmentwith a random signature encoded in the tag. While the random signaturecan be thought of as protecting the fragment, the fragment can also bethought of as simply increasing the length of the random signature andhence increasing its security. A fragment verification limit can makeverification subject to a denial of service attack, where an attackerdeliberately exceeds the limit with invalid verification request inorder to prevent further verification of the item ID in question. Thiscan be prevented by only enforcing the fragment verification limit for afragment when the accompanying random signature is correct.

Fragment verification may be made more secure by requiring theverification of a minimum number of fragments simultaneously.

Fragment verification requires fragment identification. Fragments may beexplicitly numbered, or may more economically be identified by thetwo-dimensional coordinate of their tag, modulo the repetition of thesignature across a continuous tiling of tags.

The limited length of the ID itself introduces a further vulnerability.Ideally it should be at least a few hundred bits. In the netpage surfacecoding scheme it is 96 bits or less. To overcome this the ID may bepadded. For this to be effective the padding must be variable, i.e. itmust vary from one ID to the next. Ideally the padding is simply arandom number, and must then be stored in the authentication databaseindexed by ID. If the padding is deterministically generated from the IDthen it is worthless.

Offline authentication of secret-key signatures requires the use of atrusted offline authentication device. The QA chip (which is the subjectof a number of pending US patent applications, including Ser. No.09/112,763; Ser. No. 09/112,762; Ser. No. 09/112,737; Ser. No.09/112,761; Ser. No. 09/113,223) provides the basis for such a device,although of limited capacity. The QA chip can be programmed to verify asignature using a secret key securely held in its internal memory. Inthis scenario, however, it is impractical to support per-ID padding, andit is impractical even to support more than a very few secret keys.Furthermore, a QA chip programmed in this manner is susceptible to achosen-message attack. These constraints limit the applicability of aQA-chip-based trusted offline authentication device to nicheapplications.

In general, despite the claimed security of any particular trustedoffline authentication device, creators of secure items are likely to bereluctant to entrust their secret signature keys to such devices, andthis is again likely to limit the applicability of such devices to nicheapplications.

By contrast, offline authentication of public-key signatures (i.e.generated using the corresponding private keys) is highly practical. Anoffline authentication device utilising public keys can trivially holdany number of public keys, and may be designed to retrieve additionalpublic keys on demand, via a transient online connection, when itencounters an ID for which it knows it has no corresponding publicsignature key. Untrusted offline authentication is likely to beattractive to most creators of secure items, since they are able toretain exclusive control of their private signature keys.

A disadvantage of offline authentication of a public-key signature isthat the entire signature must be acquired from the coding, violatingour desire to support authentication with a minimal field of view. Acorresponding advantage of offline authentication of a public-keysignature is that access to the ID padding is no longer required, sincedecryption of the signature using the public signature key generatesboth the ID and its padding, and the padding can then be ignored. Aforger can not take advantage of the fact that the padding is ignoredduring offline authentication, since the padding is not ignored duringonline authentication.

Acquisition of an entire distributed signature is not particularlyonerous. Any random or linear swipe of a hand-held sensing device acrossa coded surface allows it to quickly acquire all of the fragments of thesignature. The sensing device can easily be programmed to signal theuser when it has acquired a full set of fragments and has completedauthentication. A scanning laser can also easily acquire all of thefragments of the signature. Both kinds of devices may be programmed toonly perform authentication when the tags indicate the presence of asignature.

Note that a public-key signature may be authenticated online via any ofits fragments in the same way as any signature, whether generatedrandomly or using a secret key. The trusted online authenticator maygenerate the signature on demand using the private key and ID padding,or may store the signature explicitly in the authentication database.The latter approach obviates the need to store the ID padding.

Note also that signature-based authentication may be used in place offragment-based authentication even when online access to a trustedauthenticator is available.

Table 13 provides a summary of which signature schemes are workable inlight of the foregoing discussion.

TABLE 13 Summary of workable signature schemes encoding acquisitionsignature online offline in tags from tags generation authenticationauthentication Local full random ok Impractical to store per IDinformation secret key Signature too Undesirable to short to be storesecret secure keys private Signature too key short to be secureDistributed fragment(s) random ok impractical^(b) secret key okimpractical^(c) private ok impractical^(b) key full random okimpractical^(b) secret key ok impractical^(c) private ok ok key

Security Specification

FIG. 43 shows an example item signature object model.

An item has an ID (X) and other details (not shown). It optionally has asecret signature (Z). It also optionally has a public-key signature. Thepublic-key signature records the signature (S) explicitly, and/orrecords the padding (P) used in conjunction with the ID to generate thesignature. The public-key signature has an associated public-private keypair (K, L). The key pair is associated with a one or more ranges ofitem IDs.

Typically issuers of security documents and pharmaceuticals will utilisea range of IDs to identify a range of documents or the like. Followingthis, the issuer will then use these details to generate respective IDsfor each item, or document to be marked.

Authentication of the product can then be performed online or offline bysensing the tag data encoded within the tag, and performing theauthentication using a number of different mechanisms depending on thesituation.

Examples of the processes involved will now be described for public andprivate key encryption respectively.

Authentication Based on Public-Key Signature

Setup per ID range:

-   -   generate public-private signature key pair (K, L)    -   store key pair (K, L) indexed by ID range

Setup per ID:

-   -   generate ID padding (P)    -   retrieve private signature key (L) by ID (X)    -   generate signature (S) by encrypting ID (X) and padding (P)        using private key (L):

S←E _(L)(X,P)

-   -   store signature (S) in database indexed by ID (X) (and/or store        padding (P))    -   encode ID (X) in all tag groups    -   encode signature (S) across multiple tags in repeated fashion

Online fragment-based authentication (user):

-   -   acquire ID (X) from tags    -   acquire position (x, y), and signature fragment (T_(i)) from tag    -   generate fragment number (i) from position (x, y)_(i):

i←F[(x,y)_(i)]

-   -   look up trusted authenticator by ID (X)    -   transmit ID (X), fragment (S_(i)) and fragment number (i) to        trusted authenticator

Online fragment-based authentication (trusted authenticator):

-   -   receive ID (X), fragment (S_(i)) and fragment number (i) from        user    -   retrieve signature (S) from database by ID (X) (or re-generate        signature)    -   compare received fragment (T_(i)) with corresponding fragment of        signature (S_(i))    -   report authentication result to user

Offline signature-based authentication (user):

-   -   acquire ID from tags (X)    -   acquire positions (x, y), and signature fragments (T_(i)) from        tag    -   generate fragment numbers (i) from positions (x, y)_(i):

i←F[(x,y)_(i)]

S←S ₀ |S ₁ | . . . |S _(n−1)

-   -   generate signature (S) from (n) fragments:    -   retrieve public signature key (K) by ID (X)    -   decrypt signature (S) using public key (K) to obtain ID (X′) and        padding) (P′):

X′|P′←D _(K)(S)

-   -   compare acquired ID (X) with decrypted ID (X′)    -   report authentication result to user

Authentication Based on Secret-Key Signature

Setup per ID:

-   -   generate secret (Z)    -   store secret (Z) in database indexed by ID (X)    -   encode ID (X) and secret (Z) in all tag groups

Online secret-based authentication (user):

-   -   acquire ID (X) from tags    -   acquire secret (Z′) from tags    -   look up trusted authenticator by ID    -   transmit ID (X) and secret (Z′) to trusted authenticator

Online secret-based authentication (trusted authenticator):

-   -   receive ID (X) and secret (Z′) from user    -   retrieve secret (Z) from database by ID (X)    -   compared received secret (Z′) with secret (Z)    -   report authentication result to user

As discussed earlier, secret-based authentication may be used inconjunction with fragment-based authentication.

Cryptographic Algorithms

When the public-key signature is authenticated offline, the user'sauthentication device typically does not have access to the padding usedwhen the signature was originally generated. The signature verificationstep must therefore decrypt the signature to allow the authenticationdevice to compare the ID in the signature with the ID acquired from thetags. This precludes the use of algorithms which don't perform thesignature verification step by decrypting the signature, such as thestandard Digital Signature Algorithm U.S. Department ofCommerce/National Institute of Standards and Technology, DigitalSignature Standard (DSS), FIPS 186-2, 27 Jan. 2000.

RSA encryption is described in:

-   -   Rivest, R. L., A. Shamir, and L. Adleman, “A Method for        Obtaining Digital Signatures and Public-Key Cryptosystems”,        Communications of the ACM, Vol. 21, No. 2, February 1978, pp.        120-126    -   Rivest, R. L., A. Shamir, and L. M. Adleman, “Cryptographic        communications system and method”, U.S. Pat. No. 4,405,829,        issued 20 Sep. 1983    -   RSA Laboratories, PKCS #1 v2.0: RSA Encryption Standard, Oct. 1,        1998

RSA provides a suitable public-key digital signature algorithm thatdecrypts the signature. RSA provides the basis for the ANSI X9.31digital signature standard American National Standards Institute, ANSIX9.31-1998, Digital Signatures Using Reversible Public Key Cryptographyfor the Financial Services Industry (rDSA), Sep. 8, 1998. If no paddingis used, then any public-key signature algorithm can be used.

In the Hyperlabel surface coding scheme the ID is 96 bits long or less.It is padded to 160 bits prior to being signed.

The padding is ideally generated using a truly random process, such as aquantum process [14,15], or by distilling randomness from random eventsSchneier, B., Applied Cryptography, Second Edition, John Wiley & Sons1996.

In the Hyperlabel surface coding scheme the random signature, or secret,is 36 bits long or less. It is also ideally generated using a trulyrandom process. If a longer random signature is required, then thelength of the item ID in the surface coding can be reduced to provideadditional space for the signature.

Security Tagging and Tracking

Currency, checks and other monetary documents can be tagged in order todetect currency counterfeiting and counter money laundering activities.The Hyperlabel tagged currency can be validated, and tracked through themonetary system. Hyperlabel tagged products such as pharmaceuticals canbe tagged allowing items to be validated and tracked through thedistribution and retail system.

A number of examples of the concepts of Hyperlabel security tagging andtracking referring specifically to bank notes and pharmaceuticals,however Hyperlabel tagging can equally be used to securely tag and trackother products, for example, traveller's checks, demand deposits,passports, chemicals etc.

Hyperlabel tagging, with the netpage system, provides a mechanism forsecurely validating and tracking objects.

Hyperlabel tags on the surface of an object uniquely identify theobject. Each Hyperlabel tag contains information including the object'sunique ID, and the tag's location on the Hyperlabel tagged surface. AHyperlabel tag also contains a signature fragment which can be used toauthenticate the object. A scanning laser or image sensor can read thetags on any part of the object to identify the object, validate theobject, and allow tracking of the object.

Currency Tagging

Currency may be tagged with Hyperlabels in order to detectcounterfeiting and allow tracking of currency movement. Hyperlabel tagscan be printed over the entire bank note surface or can be printed in asmaller region of the note. Hyperlabel tagging can be used in additionto other security features such as holograms, foil strips,colour-shifting inks etc. A scanning laser or image sensor can read thetags on any part of the note to validate each individual note.

A Hyperlabel currency tag identifies the note currency, issue country,and note denomination. It also identifies the note's serial number, thenote side (i.e. front or back), and it may contain other information(for example, the exact printing works where the note was printed).There are two note IDs for each physical bank note—one for each side ofthe note.

Each time a note is scanned its location is recorded. This locationinformation can be collected in a central database allowing analysis andidentification of abnormal money movements and detection of counterfeitnotes. For example, in the case of sophisticated forgeries whereHyperlabel dot patterns are exactly duplicated, there will be multiplecopies of exactly forged notes (at a minimum, the original and theforgery). If multiple identical notes appear in different places at thesame time, all but one of the notes must be a forgery. All can then betreated as suspect.

Hyperlabel currency tags can be read by any Hyperlabel scanner. Thesescanners can be incorporated into a variety of devices to facilitateauthentication and tracking, for example, automated teller machines,currency counters, and vending machines. Scanners may also beincorporated into devices such as:

-   -   Currency counters    -   Automated teller machines    -   Cash registers    -   POS checkouts    -   Mobile phone with inbuilt scanner    -   Netpage pens    -   Vending machines    -   Hyperlabel Supermarket Checkout    -   Mobile Phone with Inbuilt Scanner    -   Handheld Validity Scanner

Such scanners are multi-purpose since they can also be used to scanHyperlabel tagged consumer goods and printed materials. A smallhand-held scanner may also be used to scan and validate currency. When ascanner scans a note it notifies the currency server of the notedetails, the current date and time, and the scanner location (if known).Optionally the scanner may also send the identity of the person makingthe cash transaction, if known. This information would be available inrespect of bank transactions, currency exchanges and large cashtransactions.

Currency tagging is discussed in further detail in copending patentapplication Ser. Nos. 11/041,651 (Docket number: HYN001US), 11/041,609(Docket number: HYN002US), 11/041,723 (Docket number: HYN003US),11/041,698 (Docket number: HYN004US) and 11/041,648 (Docket number:HYN005US).

Pharmaceutical Tagging

Hyperlabel tags can be printed over the entire surface of thepharmaceutical packaging, or only on a smaller area of the packaging. AHyperlabel pharmaceutical tag contains the item's product ID and aserial number, to uniquely identify an individual item. The product IDidentifies the item's National Drug Code (NDC) number. The NDC number isallocated and administered by the FDA (U.S. Food and DrugAdministration) for drugs and drug-related items and identifies theproduct and manufacturer. Alternatively the tag may contain anotherproduct ID code, such as the European International Article Numbering(EAN) code, or EPC etc.

The pharmaceutical ID can be read by a scanner and used to look updetails of the item's lot number and expiry date. Alternatively the lotnumber and expiry date may be contained in the pharmaceutical tag toallow off-line retrieval of this information by any scanner. Thepharmaceutical ID may also be used to access details such as dosage andadministration information, drug interactions, precautions,contraindications, product warnings, recall information, place ofmanufacture etc.

Each time a pharmaceutical item is scanned its location is recorded.This location information can be collected in a central databaseallowing analysis and identification of abnormal product movements anddetection of counterfeit pharmaceuticals.

Suitable scanners can include:

-   -   Cash registers    -   POS checkouts    -   Mobile phone with inbuilt scanner    -   Netpage pens    -   Vending machines

Pharmaceutical tagging is discussed in further detail in copendingpatent applications by the present applicant.

Tracking

For the purpose of tracking and item validation the manufacturer, orother central authority, maintains a database which tracks the locationand status of all items.

Hyperlabel scanners can be built into a variety of devices. Scanners maybe fixed or mobile. A fixed scanner has a permanent, known location. Amobile scanner has no fixed location. A scanner may be on-line, i.e.have immediate access to the central database, or it may be off-line.

Scanners may be specific to a particular product application, such as acurrency counter, or may be a generic Hyperlabel scanner. Hyperlabelscanners may be embedded in other multi-function devices, for example, amobile phone or PDA.

A central database maintains up-to-date information on valid object IDs,an object ID hotlist (for all suspect object IDs), and a list of publickeys corresponding to object IDs. The central server also maintains anobject scanning history to track an object's movements. Each time anobject is scanned, its timestamped location is recorded. If known, thedetails of the object owner may also be recorded. This information maybe known particularly in the case of large financial transactions e.g. alarge cash withdrawal from a bank. This object scanning history data canbe used to detect illegal product movements, for example, the illegalimport of a pharmaceutical. It can also be used to detect abnormal orsuspicious product movements which may be indicative of productcounterfeiting.

If an object is known to be stolen it can be immediately added to anobject ID hotlist on the central server. This hotlist is automaticallydistributed to (or becomes accessible to) all on-line scanners, and willbe downloaded to all off-line scanners on their next update. In this waythe stolen status is automatically and rapidly disseminated to a hugenumber of outlets. Similarly, if an object is in any other way suspectit can be added to the hotlist so that its status is flagged to theperson scanning the object.

An on-line scanner has instant access to the central server to allowchecking of each object ID at the time of scanning The object scanninghistory is also updated at the central server at the time the object isscanned.

An off-line scanner stores object status data internally to allowvalidation of a scanned object. The object status data includes valid IDrange lists, an object ID hotlist, a public key list, and an objectscanning history. Each time an object is scanned the details arerecorded in the object scanning history. The object status data isdownloaded from the central server, and the object scanning history isuploaded to the central server, each time the scanner connects.

A mobile scanner's location can be provided to the application by thescanner, if it is GPS-equipped. Alternatively the scanner's location canbe provided by the network through which it communicates.

For example, if the hand-held scanner uses the mobile phone network, thescanner's location can be provided by the mobile phone network provider.There are a number of location technologies available. One is AssistedGlobal Positioning System (A-GPS). This requires a GPS-equipped handset,which receives positioning signals from GPS satellites. The phonenetwork knows the approximate location of the handset (in this case thehandset is also the scanner) from the nearest cell site. Based on this,the network tells the handset which GPS satellites to use in itsposition calculations. Another technology, which does not require thedevice to be GPS-equipped, is Uplink Time Difference of Arrival(U-TDOA). This determines the location of a wireless handset, using aform of triangulation, by comparing the time it takes a wirelesshandset's signal to reach several Location Measurement Units (LMUs)installed at the network's cell sites. The handset location is thencalculated based on the differences in arrival times of the three (ormore) signals.

Authentication

Each object ID has a signature. Limited space within the Hyperlabel tagstructure makes it impractical to include a full cryptographic signaturein a tag so signature fragments are distributed across multiple tags. Asmaller random signature, or secret, can be included in a tag.

To avoid any vulnerability due to the limited length of the object ID,the object ID is padded, ideally with a random number. The padding isstored in an authentication database indexed by object ID. Theauthentication database may be managed by the manufacturer, or it may bemanaged by a third-party trusted authenticator.

Each Hyperlabel tag contains a signature fragment and each fragment (ora subset of fragments) can be verified, in isolation, against the objectID. The security of the signature still derives from the full length ofthe signature rather than from the length of the fragment, since aforger cannot predict which fragment a user will randomly choose toverify.

Fragment verification requires fragment identification. Fragments may beexplicitly numbered, or may by identified by the two-dimensionalcoordinate of their tag, modulo the repetition of the signature acrosscontinuous tiling of tags.

Note that a trusted authenticator can always perform fragmentverification, so fragment verification is always possible when on-lineaccess to a trusted authenticator is available.

Establishing Authentication Database

Prior to allocating a new range of IDs, some setup tasks are required toestablish the authentication database.

For each range of IDs a public-private signature key pair is generatedand the key pair is stored in the authentication database, indexed by IDrange.

For each object ID in the range the following setup is required:

-   -   generate ID padding and store in authentication database,        indexed by object ID    -   retrieve private signature key by object ID    -   generate signature by encrypting object ID and padding, using        private key    -   store signature in authentication database indexed by object ID,        and/or store the padding, since the signature can be        re-generated using the ID, padding and private key    -   encode the signature across multiple tags in repeated fashion

This data is required for the Hyperlabel tags therefore theauthentication database must be established prior to, or at the time of,printing of the Hyperlabels.

Security issues are discussed in more detail above.

Off-Line Public-Key-Based Authentication

An off-line authentication device utilises public-key signatures. Theauthentication device holds a number of public keys. The device may,optionally, retrieve additional public keys on demand, via a transienton-line connection when it encounters an object ID for which it has nocorresponding public key signature.

For off-line authentication, the entire signature is needed. Theauthentication device is swiped over the Hyperlabel tagged surface and anumber of tags are read. From this, the object ID is acquired, as wellas a number of signature fragments and their positions. The signature isthen generated from these signature fragments. The public key is lookedup, from the scanning device using the object ID. The signature is thendecrypted using the public key, to give an object ID and padding. If theobject ID obtained from the signature matches the object ID in theHyperlabel tag then the object is considered authentic.

The off-line authentication method can also be used on-line, with thetrusted authenticator playing the role of authenticator.

On-Line Public-Key-Based Authentication

An on-line authentication device uses a trusted authenticator to verifythe authenticity of an object. For on-line authentication a single tagcan be all that is required to perform authentication. Theauthentication device scans the object and acquires one or more tags.From this, the object ID is acquired, as well as at least one signaturefragment and its position. The fragment number is generated from thefragment position. The appropriate trusted authenticator is looked up bythe object ID. The object ID, signature fragment, and fragment numberare sent to the trusted authenticator.

The trusted authenticator receives the data and retrieves the signaturefrom the authentication database by object ID. This signature iscompared with the supplied fragment, and the authentication result isreported to the user.

On-Line Secret-Based Authentication

Alternatively or additionally, if a random signature or secret isincluded in each tag (or tag group), then this can be verified withreference to a copy of the secret accessible to a trusted authenticator.Database setup then includes allocating a secret for each object, andstoring it in the authentication database, indexed by object ID.

The authentication device scans the object and acquires one or moretags. From this, the object ID is acquired, as well as the secret. Theappropriate trusted authenticator is looked up by the object ID. Theobject ID and secret are sent to the trusted authenticator.

The trusted authenticator receives the data and retrieves the secretfrom the authentication database by object ID. This secret is comparedwith the supplied secret, and the authentication result is reported tothe user.

Secret-based authentication can be used in conjunction with on-linefragment-based authentication is discussed in more detail above.

Product Scanning Interactions

Product Scanning at a retailer is illustrated in FIG. 44. When a storeoperator scans a Hyperlabel tagged product the tag data is sent to theservice terminal (A). The service terminal sends the transaction data tothe store server (B). The store server sends this data, along with theretailer details, to the manufacturer server (C). The Hyperlabel serverknows which manufacturer server to send the message to from the objectID. On receipt of the input, the manufacturer server authenticates theobject, if the manufacturer is the trusted authenticator. Alternativelythe manufacturer server passes the data on to the authentication serverto verify the object ID and signature (D). The authentication serversends the authentication result back to the manufacturer server (E). Themanufacturer server checks the status of the object ID (against itsvalid ID lists and hotlist), and sends the response to the store server(F), which in turn send the result back the store service terminal (G).The store server could also communicate with the relevant authenticationserver directly.

The interaction detail for on-line product scanning at a retailer isshown in FIG. 45. The store operator scans the Hyperlabel taggedproduct. The scanner sends the scanner ID and tag data to the serviceterminal. The service terminal sends this data along with the terminalID and scanner location to the store server. The store server then sendsthe request on to the manufacturer server, which performs authentication(either itself or via a third party authentication server) anddetermines the object status. The response is then sent back to thestore server, and on to the operator service terminal.

The interaction detail for off-line product scanning at a retailer isshown in FIG. 46. The store operator scans the Hyperlabel taggedproduct. The scanner sends the scanner ID and tag data from multipletags to the service terminal. The service terminal sends this data,along with the terminal ID and scanner location, to the store server.The store server then performs off-line authentication, as described inSection 3.4.2, and determines the object status through its cachedhotlist, valid object ID lists, and public key list. The store serverrecords the scan details in its internal object scanning history. Theresponse is then sent back to the operator service terminal.

An alternative for off-line product scanner occurs where the scanner isa hand-held, stand-alone scanner. In this case the cached authenticationdata is stored within the scanner itself, and the scanner performs thevalidation internally. The object scanning history is also cached withinthe scanner. Periodically the scanner connects to the central database,uploads it's object scanning history, and downloads the latest publickey list, object ID hotlist and valid ID range list. This connection maybe automatic (and invisible to the user), or may be initiated by theuser, for example, when the scanner is placed in a dockingstation/charger.

Product scanning with a netpage pen is illustrated in FIG. 47. When auser scans a Hyperlabel tagged item with their netpage pen, the input issent to the netpage System, from the user's netpage pen, in the usualway (A). To scan a product rather than interact with it, the pen can beplaced in a special mode. This is typically a one-shot mode, and can beinitiated by tapping on a <scan> button printed on a netpage.Alternatively, the pen can have a user-operable button, which, when helddown during a tap or swipe, tells the pen to treat the interaction as aproduct scan rather than a normal interaction. The tag data istransmitted from the pen to the user's netpage base station. The netpagebase station may be the user's mobile phone or PDA, or it may be someother netpage device, such as a PC. The input is relayed to theHyperlabel server (B) and then on to manufacturer server (C) in theusual way. On receipt of the input, the manufacturer serverauthenticates the object if the manufacturer is the trustedauthenticator. Alternatively the manufacturer server passes the data onto the authentication server to verify the object ID and signature (D).The authentication server sends the authentication result back to themanufacturer server (E). The manufacturer server checks the status ofthe object ID (against its valid ID lists and hotlist), and sends theresponse to the Hyperlabel server (G). The Hyperlabel server, as part ofthe netpage system, can know the identity and devices of the user. TheHyperlabel server will relay the manufacturer server's response to theuser's phone (G) or Web browsing device (H) as appropriate. If theuser's netpage pen has LEDs then the Hyperlabel server can send acommand to the user's pen to light the appropriate LED(s) (I,J).

The interaction detail for scanning with a netpage pen is shown in FIG.48. The netpage pen clicks on the Hyperlabel tagged product. The netpagepen sends the pen id, the product's tag data and the pen's location tothe Hyperlabel server. If the pen ID is not already associated with ascanner, the Hyperlabel server may create a new scanner record for thepen, or may use the pen ID as a scanner ID. The Hyperlabel server sendsthe scanner ID, tag data, and scanner location (if known) to themanufacturer server, which performs authentication (either itself or viaa third party authentication server) and determines the object status.The response is then sent back to the Hyperlabel server, and on to theuser's default Web browsing device.

Security Tagging and Tracking Object Model

The Security Tagging and Tracking object model revolves aroundHyperlabel tags, object IDs, and signatures. FIG. 60 illustrates themanagement and organisation of these objects. As shown in FIG. 49, aHyperlabel tag comprises a tag type, object ID, two-dimensional positionand a signature fragment. The tag type indicates whether this is a tagon a common object, or whether the tag is on a special type of objectsuch as a currency note or a pharmaceutical product. A signaturefragment has an optional fragment number which identifies the fragment'splace within the full signature.

As described above, a product's unique item ID may be seen as a specialkind of unique object ID. The Electronic Product Code (EPC) is oneemerging standard for an item ID. An item ID typically consists of aproduct ID and a serial number. The product ID identifies a class ofproduct, while the serial number identifies a particular instance ofthat class, i.e. an individual product item. The product ID in turntypically consists of a manufacturer number and a product class number.The best-known product ID is the EAN.UCC Universal Product Code (UPC)and its variants. The Item ID class diagram is shown in FIG. 50.

Currency notes are identified by a note ID. The note ID comprises notedata and a serial number. The note data identifies the type of currency,the country of issue, the note denomination, the note side (front orback) and other currency-specific information. There are two note IDsfor each physical bank note—one for each side of the printed note. TheNote ID class diagram is shown in FIG. 51.

Pharmaceuticals are identified by a pharmaceutical ID. Typically thepharmaceutical ID will be an EPC. A pharmaceutical ID consists of aproduct ID and a serial number. The product ID in turn typicallyconsists of a manufacturer number and a product class number. The bestknown product ID for pharmaceutical products is the National Drug Code(NDC), allocated and administered by the US Food and DrugAdministration. The Pharmaceutical ID class diagram is shown in FIG. 52.

Object Description, ownership and aggregation class diagram is shown inFIG. 53. This is described in more detail above.

The Object Scanning History class diagram is shown in FIG. 54. An objecthas an object scanning history, recording each time the scanner scans anobject. Each object scanned event comprises the scanner ID, the date andtime of the scan, and the object status at the time of the scan, and thelocation of the scanner at the time the object was scanned. The objectstatus may be valid, stolen, counterfeit suspected, etc. If known, theobject owner details may also be recorded.

A scanner has a unique scanner ID, a network address, owner informationand a status (e.g. on-line, off-line). A scanner is either a mobilescanner, whose location may vary, or a fixed scanner, whose location isknown and constant. A scanner has a current location, comprising thelocation details and a timestamp. A scanner may be a netpage pen, inwhich case it will be associated with a netpage Pen record. If a scannerin off-line, it will keep an object scanning history, and willoptionally store a public key list, a valid ID range list and an objectID hotlist. The scanner class diagram is shown in FIG. 55.

The manufacturer, or other central authority, maintains a number ofObject ID Hot Lists, each with a unique list ID, and the time the listwas last updated. Each hot list comprises a list of suspect object IDs,comprising the object ID, date, time, status (suspected counterfeit,stolen, etc.) and other information. The Object ID Hot List classdiagram is shown in FIG. 56.

The manufacturer, or other central authority, maintains a list of validID ranges. Each valid object ID range entry in the list comprises thestart object ID and end object ID (the valid ID range) and the time theentry was updated. The Valid ID Range List class diagram is shown inFIG. 57.

The manufacturer, or other central authority, maintains a public keylist. The public key list consists of a number of entries identifyingthe public key for a range of Object IDs. Each valid object ID rangeentry comprises the update time for the entry, the start object ID forthe range, the end object ID for the range, and the public keyapplicable to each object ID in the given range. The Public Key Listclass diagram is shown in FIG. 58.

Object authentication may be performed by the manufacturer, or by athird-party trusted authenticator. A trusted authenticator has anauthenticator ID, name and details. A trusted authenticator holds a listof public-private key pairs, each associated with one or more ID ranges.This is a list of object ID ranges (identified by the start and end ID)and the corresponding public/private signature key pair. A trustedauthenticator also holds a list of secret signatures, and a list ofpublic-key signatures. Each public-key signature identifies the actualsignature and/or the padding used to generate the signature. Each secretsignature and public-key signature is associated by object ID with aunique object. The Trusted Authenticator class diagram is shown in FIG.59.

Applications

It will be appreciated that Hyperlabel tags can be used with a range ofobjects, including, for example, items of manufacture, pharmaceuticalitems, currency notes, cheques, credit or debit cards, redeemabletickets, vouchers, coupons, lottery tickets instant win tickets, oridentity cards or documents, such as a driver's licenses or passports.

The identity can include at least one of an Electronic Product Code(EPC), a National Drug Code (NDC) number, a serial number of apharmaceutical item, a currency note attribute such as a value or thelike, a cheque attribute or a card attribute such as card type, issuinginstitution, account number, issue date, expiry date or limit.

Advantages of Hyperlabel

Unlike 2D optical barcodes that are often difficult to read due to labeldamage and a direct line-of-sight' requirement needed for scanning,optically readable, but invisible, infrared Hyperlabel tags, are printedall over, or on a large section of a product label. Hyperlabel tagssupport line-of-sight omnidirectional reading. In practice, theHyperlabel reader is designed to scan the scanning field from at leasttwo substantially orthogonal directions. This helps the reader to avoidocclusions which may occur if a hand is holding an item. Hyperlabel tagsalso incorporate Reed-Solomon error correction methods to improvereliability.

A further advantage of Hyperlabels over barcodes is that they areunobtrusive to the customer as they do not use visible label space, andtag information is not restricted to only one section of a label.

Hyperlabel tags are therefore easy to locate, easy to read, and enableaccurate automatic scanning

Hyperlabels are less promiscuous than RFID tags since they requireline-of-sight for reading. This means that it will be difficult forcustomers to have their product scanned for information without theirknowledge. Hyperlabels provide customers with the means to protect theirprivacy.

Hyperlabels as Interactive Web Pages

A distinctive and unique feature of Hyperlabel technology is thatHyperlabels provide the opportunity to design packaging labels asinteractive ‘Web pages’ and thus make it possible for a whole new rangeof product-linked customer services to be introduced by thepharmaceutical industry.

When digital pen use becomes widespread, product graphics can be addedto labels to indicate interactive areas and prompting customers to writeor click using a Netpage pen. A digital Netpage pen can identify the x-yposition on a label, and enable a link to be established between theinformation on the label, and a Web page on a server. The Netpage penconnects the customer to an Internet-based Hyperlabel Server through acompanion device such as a mobile phone or computer.

Using a Netpage pen to interact with the label, customers can be offeredadditional information on drug use, risks and advice on potentialinteractions between drugs. It could also provide an opportunity forcustomers to register for participation in new drug trials, to enterpromotions, to participate in Web chat sessions, or to receive ‘free’samples. Web pages can be customised based on customer profiles, localarea health data, or by using a range of product supply chain data suchas geographic location.

Hyperlabels therefore make it possible for the pharmaceutical industryto extend the use of product labels and packaging to increase brandstrength, and to establish closer links with customers. Thus, withHyperlabels, the customer can become an integral part of the productsupply chain, and supply chain data can be integrated with customerrelationship management (CRM) or healthcare databases to improve theoverall efficiency and level of service offered to customers.

1. A system for authenticating an object, the system comprising: asensing device for sensing coded tags printed on the object, each codedtags encoding an identity of the object and a signature fragment, anentire signature being encoded in a plurality of coded tags; a processorfor determining a signature fragment identifier associated withrespective signature fragments, for generating the entire signature fromthe signature fragments and associated signature fragment identifiers,for decrypting the entire signature to obtain a generated identity;means for comparing the identity encoded by the coded tags with thegenerated identity; and means for authenticating the object using theresults of the comparison.
 2. A system according to claim 1, wherein thesignature is a digital signature of at least part of the identity and atleast part of predetermined padding.
 3. A system according to claim 2,wherein the predetermined padding is associated with, and unique to, theidentity.
 4. A system according to claim 1, wherein the coded tags areprinted in invisible ink.
 5. A system according to claim 4, wherein thecoded tags are printed substantially coincident with visiblehuman-readable information on the object.
 6. A system according to claim1, wherein each coded tag further encodes a position of the respectivecoded tag on the object, wherein the respective signature fragmentidentifiers are determined from respective positions of the coded tags.